It's a lot like regular keyword advertising--only better, since you're charged only when a customer actually makes a call or orders something.
Select categories and keywords
Visit a site such as ingenio.com or snap.com to choose the categories and keywords you think customers will use to find you.
Bid for placement
Determine how much you're willing to pay for the action--say, a phone call or an online order. The higher the bid, the better placement ads will receive on the search results page.
Pay for the action
When a customer dials the phone number listed on a pay-per-call ad--or, in the case of pay per sale, buys something--the advertiser's account is automatically charged or a charge is added to a monthly invoice.