Tickets are $5 each. You buy as many tickets as you want (hopefully, that's a large number of tickets), and then place your tickets in the lot(s) you wish to win. There's one big drawing at the end when all the lots are drawn. For new folks, it is tradition to boo Os if he wins.
I've heard people in the past saying it's not worth entering the raffle because "only big rollers who buy 100 tickets will win." This isn't right at all. First, people should enter because it's for the children of Greensboro. Second, there have been many winners in the past several years who have bought 4, 10, or yes, 20 tickets.
TL; DR: bring a lot of cash.