In Tinyfolks one can train each of the normal folks into specialized classes. Each folk can be trained up to two times and each combination of training schools is allowed (so sword + holy for example, or 2x sword as well).
The guide will feature all combinations and skills possible.

Please feel free to add comments if you catch errors I made during copying this information from the game or if you have any additional feedback.

The folk is a special class, as it is the complete base class with no specialization. Don't be mistaken tho, the folk is a very effective all-rounder class, which can carry its weight during a majority of the game.

Base classes are specializations that take only one training and can only be trained from normal Folks.

1x Sword Training [Barracks].
Warrior is a nice early class that enables multiple enemy targeting as well as high damage output. Also scales very nicely with weapon damage.

1x Shield Training [Barracks].
Guard is a class that excels at soaking up damage, but otherwise not so useful as the weapon upgrade only upgrades defensive values and not attack values.

1x Scroll Study [Magicarium].
Apprentice is a weak mage that has some skills to inflict status effects on enemies as well as some AoE spells.

1x Faith Study [Temple].
Priest is a very nice early game healer with strong single and multi target heals.

1x Hunting Practice [Camp].
The Range is a nice damage dealer against enemies in the back, as well as bosses. Doesn't work well against front-row enemies.

1x Night Shift [Slum].
Thugs can help stunning high value targets and reduce their stats.

2x Sword Training [Barracks].
The Berzerker is a high damage dealer for front-line enemies, scales very effectively with weapon damage.

2x ShieldTraining [Barracks].
The Tank is the best char for soaking up damage, but again has no weapon to upgrade for damage.

2x Scroll Study [Magicarium].
The Wizard has an enormus amount of AoE spells that allows for very effective enemy clears. Also scales very good with weapon upgardes.

2x Faith Study [Temple].
The saint has better group heals then the priest, but is harder to play right.

2x Hunting Practice [Camp].
High damage dealer for bosses but also very effective at removing single targets. Scales very effectively with weapon upgrades.

2x Night Shift [Slum].
Very effective at de-buffing and stunning one target and also comes with some survive-ability.

1x Sword Training [Barracks].
1x Shield Training [Barracks].
The Knight combines offensive with defensive capabilities, making him a good all-rounder.

1x Sword Training [Barracks].
1x Scroll Study [Magicarium].
Can go very heavy on status effects, like poison, bleed and burn.

1x Sword Training [Barracks].
1x Faith Study [Temple].
Very balanced character that can buff itself offensive and defensive and deal damage to single and multiple enemies. Sadly the default attack also moves the target.

1x Sword Training [Barracks].
1x Hunting Practice [Camp].
Basically a worse Hunter lol.

1x Sword Training [Barracks].
1x Night Shift [Slum].
Has a nice stun with damage skill, making him an effective single target handler.

1x Shield Training [Barracks].
1x Scroll Study [Magicarium].
The Warmage has a lot of offensive and defensive buffs.

1x Shield Training [Barracks].
1x Holy Study [Temple].
Nice effective tank which can also heal. Sadly again only a shield therefore no weapon (and heal) upgrades without artifacts.

1x Shield Training [Barracks].
1x Hunting Practice [Camp].
Nice alternative to the Hunter if one values the defensive debuff.

1x Shield Training [Barracks].
1x Night Shift [Slum].
If one has no access to weapon upgrades it is a nice class, but the Ninja has no weapon so he cannot be upgraded.

1x Scroll Study [Magicarium].
1x Faith Study [Temple].
Can restore power, can heal and can deal damage. What's not to like?

1x Scroll Study [Magicarium].
1x Hunting Practice [Camp].
Can apply and remove debuffs as well as healing and AoE damage. Doesn't scale that well with weapon upgrades.

1x Scroll Study [Magicarium].
1x Night Shift [Slum].
Surprisingly effective damage dealer with sustain.

1x Faith Study [Temple].
1x Hunting Practice [Camp].
Also a very nice healer and damage dealer combination

1x Faith Study [Temple].
1x Night Shift [Slum].
A nice option if one does not have access to weapon uogardes, as the sage has no weapon to upgrade. Nice damage and utility spells.

1x Hunting Practice [Camp].
1x Night Shift [Slum].
Some status effects paired with damage. Doesn't scale well with weapon uogardes.

The King is a special class as it cannot be trained to anything else and one only has one king/queen per game. The King is surprisingly potent if one can upgrade the staff at the magicarium.

The Troubadour is a special class as it cannot be trained to anything else and can only be acquired from the Tavern. He comes with no weapon to upgrade. He is quite useful tho.