That's quite a lot of information you're asking for there, Sheo. The details are quite hotly debated, and one could write a very long post in order to cover them all comprehensively.
I'll summarize for you as best I can: The police selectively edited some surveillance footage from a local convenience store to make it look like Brown was a thug, but the owner of that store later vouched that Brown didn't bully anybody or steal anything. There was a disagreement between Brown and store clerk that got heated for a few seconds (something about the clerk refusing to accept Brown's payment, IIRC) during which Brown shoved the clerk, but it ended peacefully and Brown paid for the stuff and left.
The police account of the confrontation is that Brown attacked Wilson, ran away, and then turned back around and charged at him. Other witness accounts seem to indicate the exact opposite. Forensic evidence supports a mix between the two stories, but there was no evidence or testimony that I'm aware of besides Wilson's own word that Brown ever attacked him. The guy who was walking with Brown says that Wilson pulled up right next to them and pulled Brown into his car window. One thing quite clear is that Wilson's account is lying about multiple details, but not anything that points to one side or the other's story being conclusively the correct one.
Personally, I'm much more inclined to believe it was Wilson that attacked Brown, but I'm very cynical about police in the U.S. Go ahead and ask if you have any more specific questions, but I would suggest looking up fact-based sources on your own to get a better impression of what the issue looks like.