A character can have up to 3 professions. Professions are either gathering or production (my words, not theirs). Gathering professions include mining, foraging, and butchering. Production professions include runebreaking (adds extra stats to items), outfitting (cloth/leather goods and armor), weaponsmithing, blacksmithing (chain/plate goods and armor), apothecary, and artificer (staves, wands, and other accessories).
You gather things from the world and use them to craft known recipes... You can augment those recipes with items you get from rifting.
The items you craft are of good quality and are usually better than the quest items around that level.