To be completely honest you technically don't really need to know anything. You can know squat about witch craft and do a spell. The only downside it's you'll have no idea what you're doing. So just do research on different topics and you'll just pick things up as you go and start to build up a foundation for your knowledge. That's how I'm doing it. Some good things to know include
-correspondences of incense, moon phases, different herbs, candle colors, etc.
-the meaning of intent
-have a general understanding of energy, the way it flows, manipulation
-also meditation!! Try meditating in order to better focus your intent and such.
Hope this helps!!!