Maybe you know this situation: You find an interesting software that is worth to play. After you’ve installed it there are two possibilities: either the software is (a) very easy and self-explanatory, or (b) it is very complex.
As most software fall into category (b), one way to get used to it is you can play around and discover it by yourself. Sometimes it works, sometimes not. In case you need help, you can either ask a programmer, or write a post to a mailinglist or forum. But when you need an answer for your question now what else remains? Right! You need documentation!
And with documentation, I mean good documentation. Not something with “Documentation? Use the source!”