This is Chapter Four of the Wasteland Survival Guide, found here:
http://steamproxy.net/sharedfiles/filedetails/?id=553553264

I got a request from my other guide to cover how power, lights and assigning settlers to jobs worked, so I went and decided to cover the entire settlement topic. This guide will explore every single aspect of the mechanics on how settlements in Fallout 4 work, as well as several tips and tricks on how to make it efficient without taking too much time. If you find any inconsistencies or you think you can improve on how I explain something, please notify me in the comment section.

To assign a settler, press E on him in build/workshop mode and press E again to assign.

A settlement can only be founded where there is a workshop. This can be found on the map, if you hover over an explored icon on the map, there may be a NPC count and a happiness rating. This means this area can support a settlement. To access the workshop UI, hold V by default while in range of a workshop (the range of a workshop can be seen inside the workshop UI as green lines). To scrap items, see my other guides.

Beds
Each settler requires one bed to be satisfied. Luckily, these are cheap. Cloth and wood/steel are very common and this shouldn’t be a problem. To place one, hold V by default, go into ‘Furniture > Beds'.

Water
Each settler requires one unit of water to be satisfied. Go into Resources > Water and place a bunch of water pumps. These water pumps must be on the ground and cannot be indoors. Excess water units that your settlers are not using will be automatically be converted into purified water and be placed in your workshop inventory.

Food
Each settler needs one unit of food. The Sanctuary settlement starts off with melons, so simply harvest them and plant them from Resources > Food, and find the harvested melons. This takes some time in the beginning to achieve, however, if you are impatient there are various plantable fruits in the Super Duper Mart, in the wooden containers. You need a settler to plant and harvest.

Placing items through the workshop UI
Sadly, there is no extremely precise way of placing things. Left and right mouse button to rotate, E to build, and R to scrap. Walls and various structures snap to each other, but this can be annoying if you want to have a slight difference as it will force you to snap. I don’t know of any other way to do it.

Hold E over an item, to pick up the item as well as everything attached to it. However, it will also move anything close to it. Thanks to nome22.

There is a random chance that an attack by bandits or other parties may attempt to raid your settlement, therefore it is important to equip your settlers with guns and some ammo, as well as placing defenses. The defenses can be found in the defenses tab, and include fortifications, turrets and traps. I recommend using the ‘structures’ tab with the defenses to create a fortifiable base. Defense points currently don’t seem to do much but provide an indication on how fortified a settlement is. For maximum happiness, make sure your defense rating is more than your food + water rating.

Guard Posts
Guard Posts offer 2 Defense points each. However, it must be active for the points to be added. To assign a settler to guard (or to do anything in general), press E on default in build/workshop mode on the settler to command, and press E again to assign him on the post you want him to guard. I don’t recommend placing many of these as well placed turrets and traps are almost better in every circumstance to utilise your settlers better.

Turrets
Just place them and they shoot at things, while giving defense points. Keep in mind, however, that they do have a range and specific turrets work better in different situations, for example, the flamethrower turret in closed tight hallways. Some turrets require power and I will cover this in a different section.

Traps
Traps are situational, and all traps require power. They have an AOE effect, but personally, I like turrets better. I’ll cover power in the next section.

Power is fairly expensive, and you will constantly run out of copper from running wires and pylons everywhere. However, the power system in Fallout 4 is impressively diverse, and many different things can be done with all the different pylons. However, I will be only covering the base pylons.

Generating Power
This is simple. Simply place generators.

Making a power grid and connecting power
Press space on the generator, then press space on the thing you want to link to. However, there is a limit on the range, and this is where power pylons come into play. Link the generator to the pylon, and you can link the pylon to another pylon to increase how far the power field can extend to.

Items requiring power
Some items require power to run, like the settlement recruitment tower. If you select a blueprint, it will tell you if it has a power requirement. If it has no number and just shows a lightbulb sign, it does not need to be connected to a pylon to run, simply be in range. If it has a number, like the recruitment radio tower, you need to run a wire to the tower from a pylon in order for it to be running.

Power can be used to run and make very complex traps and contraptions.

I'll keep this short and concise. To attract settlers to your settlements, you can setup a Recruitment Radio Tower, found in Power. Link this up to power sources, turn it on and in your Pip Boy, you should be able to find the radio signal. If it is on, that means settlers will go to your settlement over time.

Happiness goes up over time if you have all needs fulfilled = beds, food and water. It is slow and gradual. If you don't have the needs fulfilled, happiness will go down. Make sure that your total defense rating is equal or more than your food and water number combined.

To make sure your happiness is going up, or to find out the reason why your happiness is going down, talk to a few of your settlers. They will complain about aspects of your settlement (etc nightmares if you have low defence, hungry if you have low food).

Most of the settlement features are locked behind the 'Local Leader' perk, in the Charisma tree.

Settlement Trading
You require at least Charisma level 6 to get the first level of 'Local Leader', which unlocks settlement trading.
How settlement trading essentially works, is that resources are shared between the two settlements, making it so that you can use one settlement's resources in another to build or modify.
Each 2 settlements you want to connect requires one settler to run. Once both settlements are connected, you can use the resources from another settlement in modding, or building, but you can't directly access the storage bin.

To assign a settler to trade, press Q on the settler to bring up the supply line menu. Remember to have the Local Leader perk.

The second level allows you to make stores, which can range from general stores to medical
clinics. What this does, is that it makes money for your settlement (and various items if you have weapon/armour/item traders) over time based on your population and happiness. Each store you run requires one settler.

Charisma
The settler limit in a specific settlement is calculated by (current charisma level) + (items you are wearing that boost charisma) + 1(If you have the charisma bobblehead) + 10. Confirmed by nome22. Therefore, it is important to wear items that increase charisma and that you upgrade your charisma in S.P.E.C.I.A.L stats if you want a large settlement.

The Scavengers Bench allows a settler to be assigned to it, and that settler will then 'scavenge' for items. Items will be automatically added to your workshop bench.

The bell is useful, as once rung, all settlers in a settlement will go to the bell. This is useful for rollcall, and defense during settlement raids.

Stores require local leader level 2, but allow you to sell directly to people at your settlement, and strengthen your settlement web's economy. It also adds a meager amount of bottlecaps to your workshop inventory as tax over time.

The 'Magazine Rack and Bookshelf' buildings allow you to show off your collected magazines.

The Bobblehead Display allows you to display bobbleheads (as alluded in the title)

- Make a home base. This is very useful, as you have a place to store your useful loot, and have a place you can fall back to. It will make your life easier.

- Make sure to get the Local Leader perk ASAP if you're focusing on settlements. Yet again, makes your life easier.

- If you need a flat area, lay some flooring down (under Structures > Wood > Floor), and walls and other stuff will automatically clip towards them.

- If you mouse over a settler, the item they are assigned to (bed, store, crop etc) will be highlighted in the UI color.

- If you aren't sure who has a job and who doesn't, assign a settler that is currently working on food, as settlers get automatically assigned to food if there are slots avaliable.

- You can trade with your settlers by talking to them, and give them armor and weapons to use. Doing this with your provisioners will allow you to have a safe wasteland.

If this guide has helped you, rate it up!