You can't wait until you understand it to begin. Much of your understanding will come from the changes you see in your child and in your own thinking, and in your relationship with and perception of learning itself. You can't read a touch and then go and unschool for a year and then come back and see what you did wrong; you could be a year in the wrong direction.
Read some, do some. Think. Rest. Watch your child directly and as clearly as you can...
The books that have helped us with unschooling have been things that amused or intrigued or provided answers to questions. How-to and trivia books have been popular here. Real-life combined with humor makes for easy learning.
Given a choice between something funny and something somber, go with funny if your goal is peace and learning. Very few things need to be still and serious.
If you're going to unschool, it needs to be better than school. If that involves getting mental, emotional or physical therapy for the parents, then do it! The house doesn't work if the roof is leaking and there's no heat. Parents don't work if they're in an emotional fog and can't pay sweet attention to their kids.
Healing Presence photo by Sandra Dodd, of some ice cream in Leiden
Did you do something to make a child's life better and richer? Be grateful that you thought to do that, or know how to do that. Did your child look at you with affection? Can you tweak your life enough that those affectionate looks come even more often?