The pimping mission consists of driving prostitutes around San Andreas to meet their respective customers.
Upon collecting a prostitute after a successful session, she will give you a $300 cut off her fee. The more times you do this without stopping or failing the mission, the greater the "multiplying" factor, so after 2 drop offs the cut you receive is doubled to $600, after three it is tripled to $900 and so on.
On completion of the "pimping" mission prostitutes will pay you to sleep with them. The mission can be repeated any time by entering a Broadway car.