Classes are gained by using your 3 breakthrough points. You can choose 3 classes out of 8. These are the trainers marked on the map as "spellblade trainer", "sage trainer", "monk trainer", "mercenary trainer" and so on. You only get 3 points so you have to choose wisely, and they are the skills that cost 500 silver and give you access to the top class skills of that class. Hope that makes sense. Check out the trainers next time and give it a look. The breakthrough skills are in the middle of the skills panel, with a 500 silver and 1 bp point tag on them, and they connect the bottom panel of skills that anyone can learn to the top panel which are the class specific skills.
Crafting is quite good, but it's as deep as you want it to be. Basic crafting is making a campfire, maybe using a cooking pot to make food or an alchemy kit to make potions. You can craft armors and weapons if you want, or choose to find them or buy them instead. It's very open in how you approach the game, you can do whatever you like and figure out a way to improve your character. There are recipes in the game as well. It's not too complex, but there are a ton of recipes you can learn which usually require 2 or 3 ingredients to make. It's a fun, rewarding and non-intrusive system like the survival aspects are too.
There are also rare ingredients and there are a ton of things you can make. Healing potions, different meals with different buffs, traps, rags and varnishes to add an elemental damage to your weapon, armor, weapons, all manner of other potions as well. There's a lot to it but it doesn't take much, you don't even have to find a workbench or anything, just manually make it with your hands. Also, certain vendors craft rare armor and weapons if you bring them certain ingredients and enough silver (the game's currency). They'll craft you really nice stuff but the ingredients may be rarer to come by.
I usually craft Life Potions, Astral Potions, Fang Weapons, maybe a meal here or there. I've had the blacksmith in Cierzo craft me Blue Sand Armor, which was pretty nice. I also craft makeshift torches to use with my Flamethrower spell. And if refilling your explorer lantern attached to your backpack is considered crafting I do that as well. I haven't gone too deep with it but my playstyle doesn't require it much at the moment. You'll create your own unique way of doing things in the game that is 100% unique to you and what you want to do.