Excellent question! I would recommend this great thread that was written up not too long ago: Amy's guide to the minimum your character should know.
It’s a mixture of OC and IC information, and gives a really good overview of everything. It also includes links to further reading on the different topics covered, should you want or need more detail.
It’s okay to feel a bit overwhelmed by it. A lot of us approached the game in the same way, thinking we needed to know EVERYTHING, before realising that nobody cared if we didn’t - because nobody else does either!