What part/s confused you?

There really isn't a single most important thing to work on. Some OoC's are heavily formatted and hugely detailed, while others are rather rougher around the edges. As I've said before, find an OoC in the section that you're working in and look at what they do. If you find one that you like, copy its structure but change the information so that it applies to your game.

I'm afraid that there isn't a right answer or any one way of doing it that's better than all the other ways, but, on the other hand, there's no real 'wrong' way of doing it. I've seen messy, badly-organised OoC's for hugely popular games and nobody's going to kick you off the forums because you made a messy OoC. Just look at what other people do and give it a go yourself. If it doesn't work out, you can always try again.