You are always red, neutral buildings are grey, and any other colours are enemies that will try to defeat you.

Attack by selecting one or more of your buildings by clicking on it - they will get a yellow highlight around them, which you can deselect by clicking again.

Double click to move units from one or more of your buildings into another of your buildings, be careful after doing this as sometimes the building you moved to is highlighted afterwards, so you might want to click that off once the move has started if you don't want to move units back away from the target whenever you move next.

Conquer all non-red and non-grey buildings to win a level, and then either play it again but harder up to five times, or move onto a new level. Or possibly play the same level over and over for extra gold/stars each time you do so, as well as progress towards some of the in-game achievements that also give more gold/stars eventually.

Buildings come in five levels, each level increases the troop capacity by 10 up to a maximum of 50. Once a building reaches its limit an upgrade bar will tick away (slower for higher levels), and once done the capacity will increase by 10, and then the building will start filling that up (apart from Towers which doesn't generate any new troops).

Temporarily you can overstock a building above the 50 cap although the excess will continually be reduced, this can be useful either when a big wave of enemies is about to hit your building, or to send your regular troops into a Smithy or Stable and then quickly send them out having been converted into stronger or faster troops because they now count as coming from that building.

Note that upgraded buildings only have increased capacity, they do not generate troops any faster (Towers again being the special case that have an increased area of effect for its ability, but all levels of Tower do not generate any new troops).

If one of your buildings has more than the current capacity the excess will die off fairly quickly, but the progress bar to upgrade will go much faster so you can send 80 or so troops to a level 1 building and get it up to level 5 if they arrive roughly at the same time.

If you reach a stalemate on a level after a while the morale spell in the bottom left and/or the war trophy spell in the bottom right will become available to cast for free - these accumulate over time and by killing enemies (morale) and capturing buildings (war trophy). If you can't wait you can spend one of the stars accumulated by winning previous levels to cast either spell at any time. As you can replay any trivial level at any time to earn more stars (and the achievement is based on total earned whether spent or not), the only penalty is to not get to use them later on generally harder levels unless you spend time farming more stars. But you will probably need to farm cash for upgrades, so although you probably don't want to spend them needlessly, you are unlikely to run short of them unless you really want to push the higher levels without doing much farming, and are using several for every level completed.

Still farming gold for improving your troops permanently via the upgrade system discussed later is the better way of making the harder levels a bit easier, but those bonuses only slowly accumulate over time so aren't going to help with clearing an awkward situation on a particular level, which is where spending the stars can help.

Barracks

These have a rounded dome on top. Your basic building that provides no special benefits, all other buildings are described compared to this.

Castle

These have crenellations from level 2, at level 1 they are just cubes with rounded corners. Units in these buildings defend twice as well as in a barracks, but have no offence bonus when sent out.

Smithies

These have a horns on the roof. Units sent out from these buildings do double damage when attacking the target building. They have no defence bonus.

Stables

These have a pointed roof. Units that attack from stables have a base speed of double that of a barracks, but do not otherwise gain a defence or offence bonus. They are good for attacking towers or going past them, as they spend less time in the attack radius.

Tower

These have a large crystal on the roof. Any enemy unit passing through the glowing area take casualties a few times a second, however once the enemy reaches the tower they otherwise defend as normal (although the tower will keep killing the reinforcements as they arrive) and have no offence bonus if sent to attack. Unlike all other buildings the Tower does not replenish the troop numbers automatically, and this also means to upgrade it you will need to send more troops from other buildings repeatedly, or just send a lot at once and hope it is enough. If attacked you will need to reinforce the numbers lost from another building or it will be more vulnerable to later attacks.

As well as increasing capacity in the same way all other buildings do, increasing the level increases the range of the Towers effect - note that once it is level 5 the range will not reduce even with less troops (either defeated by enemies or sent to attack) unless the building changes hands, so you don't less area of effect or have to level it up again as long as you hold on to it.

In the bottom left corner is a icon with crossed swords indicating the upgrade area. Using the gold from winning levels you can improve your troops in various ways.

Each upgrade type has a basic and super version, the basic is always active and costs 500gp + 250gp per previous level - so +1% is 500gp, +2% is 750gp, +3% is 1000gp, etc. The super upgrade for most of the boosts affects how long the temporary spells take affect with 8 seconds being the base, 9 seconds costing 1000gp, 10 seconds for 2000gp, 11s is 4000gp. The War Trophy and Morale boosts are slightly different, these increase the passive progress of the spell casting bars from taking 360 seconds to complete, to 345 seconds for 1000gp, 330 seconds for 2000gp, 315 seconds for 4000gp, etc.

Note that for the Super spells, Strength Speed and Defense are cast after accumulating enough Morale, where Armor, Attack and Growth are cast from accumulating enough War Trophies. Given you have to pick one of each group of three to cast each time, it may be worth concentrating on levelling the one in each group you use most rather than spreading out the upgrades equally - the obvious example being Growth which is always useful, whereas the other two options only affect Towers which not all levels have (and even when they do, they aren't always that important depending on the positioning). Strength, Speed and Defense it is not so clear, Speed is great for attacking towers or through tower zones, but Strength is great for taking down those key castle locations. However while permanent/basic Defense is great, a few seconds of extra Super Defense is probably not as useful as improving Super Strength or Super Speed's durations.

Wizard - Blue:
Armor of Troops: This increases the damage resistance of your troops to towers area of effect damage by 1% per time bought.
Super Armor of Troops: If you cast the super armor spell (+200%) it will last longer by 1 second per time bought.

Warrior - Red:

Strength of Troops: This increases the damage your troops do when attacking any building by 1% per time bought.
Super Strength of Troops: If you cast the super strength spell (+200%) it will last longer by 1 second per time bought.

Archer - Green:

Speed of Troops: This increases the speed your troops move at when attacking any building by 1% per time bought.
Super Speed of Troops: If you cast the super speed spell (+200%) it will last longer by 1 second per time bought.

Druid - Grey:

Defense of Buildings: This increases the defense of your buildings will when attacked by 1% per time bought.
Super Defense of Buildings: If you cast the super defense spell (+200%) it will last longer by 1 second per time bought.

Necromancer - Orange:

Attack of Towers: This increases the rate at which your towers will enemies inside their range by 1% per time bought.
Super Attack of Towers: If you cast the super attack spell (+200%) it will last longer by 1 second per time bought.

Priest - Yellow:

Growth of Buildings: This increases the rate your buildings generate new troops by 1% per time bought.
Super Growth of Buildings: If you cast the super growth spell (+200%) it will last longer by 1 second per time bought.

Merchant - Cyan:

War Trophy: This increases the rate you generate mana by capturing buildings to allow you to cast a free war trophy spell (bottom right corner) by 1% per time bought.
Super War Trophy: This reduces the total time it would take via passive mana gain to cast a free war trophy spell by 15 seconds per time bought (starting at 360 seconds).

Alchemist - Purple:

Morale: This increases the rate you generate mana by killing enemies to allow you to cast a free morale spell (bottom left corner) by 1% per time bought.
Super Morale: This reduces the total time it would take via passive mana gain to cast a free morale spell by 15 seconds per time bought (starting at 360 seconds).

The primary thing that wins levels is getting more (non Tower) buildings so you are generating more troops per second than the enemy.

The next most important thing is trying to set up a situation where they enemy is attacking your castles, or anywhere that requires him to pass through your (or even an third enemies) Tower area of effect - although ideally not directly attacking the tower as that requires micromanagement replenishing the towers defenders. Whether these are possible to do depends on the layout of the level.

Timing is important - if you attack with all your buildings onto a single target they will arrive in a spread out pattern. If you can start with the furthest building(s), then closer buildings to the target as the existing crusade pass them, with fast troops needing to be delayed even further. This gives the target building less time to regenerate defenders between your attacks, this is particularly critical for taking castles as each defender regenerated is worth double, and in a case where an enemy AI is reinforcing a castle if you can flip it to your control by a big enough group of attackers at once you will start to get the double defense bonus instead of the enemy, reducing your loses during the fight for control of it.

The other part of timing is to take advantage of weakened buildings and avoid attacking contested buildings while they are full strength. For example on level 8 typically you take the top right barracks immediately with 2 waves from your two starting barracks, then after a few seconds take the top middle barracks. Then you wait for the AI to knock the castle down to around 5 troops and try to time your attack to arrive as soon after the last of his troops are defeated as possible. Then when he futilely attacks your 30/40+ castle all four barracks send troops to take one of stables while they are below full strength, and so on.

One thing to learn is the AI - on the first couple of difficulty levels the AI is fairly dumb, although it always knows where your troops are attacking as soon as you send them out (although it may wait to reinforce the target until the last moment). At higher levels the AI will basically always reinforce when it knows it would otherwise lose a building, and knows if it has enough to take your buildings to a very accurate degree (generally almost every attack on unreal difficulty will take a building with just a couple to spare), so apart from taking advantage of attacking non-castle buildings in order to strip the castle's defences and allowing you to take it much easier, the main way to win is to out produce troops or have a better match up of building types. Sometimes you can break deadlocks with the triggered abilities, and in the worst case just come back once you have upgraded a lot more.

The AI will also tend to attack weakened buildings where it can, but otherwise it seems indifferent to where it is attacking, and the AI seems to attack other AI buildings just as frequently as it will yours all other things being equal, so another thing to be aware of is when taking a building that is the only place where one or even two AIs can then attack can be a problem, as you will be under continuous siege until you can knock one of the enemies out of the game - and it is usually far better to do so than advance on multiple fronts unless you can take a defensible location against one AI and then switch to knock the other(s) out before finishing off the first one.

Note you can also pin down AI forces, it seems like if you send in even a small amount of troops to a building, the AI will not send out any troops from that building until they have arrived and been defeated, so you may be able to use some remote barracks to continually send whatever small force it can muster to attack one building with its 50 troops while your main force attacks another that should no longer be able to get reinforcements. Of course this doesn't help when the enemy buildings doing the reinforcing are behind the target as you can only attack the first enemy (or neutral) building on each route available at any time.

There are a large number of in game achievements, most of which give both cash and stars (essentially except the ones for earning a certain amount of cash or stars only give the other currency). Each has 5 different layers with higher targets and higher rewards, with the 5th and final target also being a steam achievement (sometimes with a different name), if they work for you, they don't seem to trigger for me.

Note that only the gold/stars for the first target is given, the later levels are always a multiple of the first - so if it is 500/1 star for the first target, the second will be 1000/2, the third 1500/3, then 2000/4 and finally 2500/5.