Do book stores buy my books, or do we split the profits?

Just curious. Say I'm self publishing a book, and the big stores (Barnes and Noble, Borders...) want it, do they pay for it first or do they split the profits? Say they buy each book for 10 dollars, and they want a thousand copies. Do they give you $10,000 and then you give them all the books? Or do you give them a thousand books, and get money from each subsequent book sale? Pardon my English... lol