PPC…looking for a brief introduction.

Before I start, I’d like to thank everyone who participates in this forum for sharing their knowledge…it has been very helpful to me.
That said, I’m looking for an explaination of a concept I haven’t wrapped my head around: paying a PPC company (broker/vendor) for the right to put a link on your webpage only to have them pay you back XX.xx $’s for yy clicks. This form of marketing/bartering is new to me. Also, can someone touch on the bidding process involved in PPC programs?
Thanks much

Original post by Brokenspear