First bonfire of Huntsmans copse, the cave behind you should have an NPC in a Chair. If you have certain Faith and Int Requirements (8/8 I think) then you can talk to him and buy hexes and he will also give you stuff if you have more than base requirements for a lot of hexes. Later on there is a covenant that specializes in Dark, as covenant rewards you will get Hexes and Chimes, and can also purchase more.
Ty. So do I need faith to use dark spells? I smell a respec if so