It's an auction. There are 9 ad slots in total.
Let's assume you want to buy 3 slots. You bid "3 @ 0.02" (3 slots for 0.02
BTC each, so you will pay a total of 0.06
BTC for the 3 slots). The higher bid for every slot at the end of the auction will win and get them.
In your case, you will be "fighting" with the users who want to buy a slot. Let's assume you want to buy a slot in the
current round (the user "lightlord" bidded all 9 slots for 0.02
BTC each), so you have to bid 1 slot for 0.04
BTC (or higher). If no one bids this slot for a higher price, you will get it at the end of the auction.