In a big book meeting they'll kick off with the formalities and any announcements. Then they'll read a bit of the big book (taking turns to read, but likely you'll choose not to do so for the first meeting). Then the people at the meeting take turns to share back their thoughts on what was read out.
The good thing about a big book meeting in my opinion is that the people there will all be there because they take their recovery seriously and work their program. If you decide to pursue AA and decide to get a sponsor at some point, a Big Book meeting is a good place to find one. They're often the saner meetings.
Often BB meetings have chips as well (not the ones with salt n vinegar, the little metal kind) so you may get a 24 hour chip. I kept mine in my pocket for a good while.