Regular soap does not usually kill bacteria outright, but it can be a very effective way to remove them from skin and from other surfaces. In routine hand washing, using soap increases the amount of time most people spend washing, which makes the hand washing more effective. Also, soap is a surfactant, which means that it allows the water to mix with and remove skin oils that bacteria cling to. Because of its surfactant qualities, soap helps to eliminate large numbers of bacteria from the skin.
Antibacterial soaps have recently come under fire because they are suspected of unbalancing the normal flora of the skin, and of possibly increasing the chances of developing resistant bacteria. Regular soaps do not contribute to these problems.