not sure how adbrite works

hi, i just recently swtiched to adbrite to try it out and see how it works out compared to adsense and was wondering how it actuallly works, because my site still has the "advertise here" thing going where the add should be.
do people acually have to sign up to advertise on MY site before ads start showing up or does adbrite just automatically handle and put the ads up like adsense?
thanks in advance:)

Original post by michiganfootball20