To create a creature you need to find a necromancer (which happens fairly early) as well as a crystal skull (which will take awhile longer). Either as random loot, or from certain chests or quest rewards, you will find various body parts with different properties. The head, for example, determines the class (fighter/ranger/mage) and can have skill bonuses (Rush Attack, Magic Missile, etc); the arms can have hitpoint and/or melee/magic damage bonuses, the torso determines melee/ranged/magic resistances, and legs have Conditioned Body / Indomitable Will / Heightened Reflexes bonuses.
You should have a few parts by the time you get the crystal skull, but if not the necromancer will have a basic version of everything required. You can sell duplicates or weaker pieces as you find better ones, before talking to the necromancer (once you can create a creature, the necromancer will automatically add any body parts in your inventory to the available options when creating the creature).
Enchantment requires an enchanter (located not too far from the crystal skull location, actually), formula and gems. You will find various weapon/armour/jewelry enchantment formula, or if you have an item with an enchantment you can get the enchanter to un-enchant it to acquire the formula (you don't recover the ingredients, though). There are various ore veins where you can get gems and minerals, or they can be bought or found, etc.
Alchemy requires an alchemist (in the starting village in Broken Valley), potion formula as well as various plants as ingredients. Some plants can be picked, or they can be bought or gotten as random loot. The enchanter and alchemist will both take any new formula you have in your inventory when you talk to them.
About half way through the game you acquire a battle tower, containing an enchanter, alchemist, necromancer and trainer (who can raise the level cap of skills) for easy access. You will also have runners, who you can send out to get gems or plants for you.
Character Optimization - some spoilers in the follow-up discussion, IIRC mostly mentions of various combat techniques for several boss type opponents
The history is described throughout the game (in dialog as well as several series of books), so you don't need to have played either of the previous Divinity games, but:
can someone sum up the story.
Anything else?
Welcome to the forum.
