You need to file Form DS-160, then pay the VISA fees and make appointment with your nearest consulate for interview. These are the basic things one who seeks non-immigrant visa should do.
From your other question, I know that you will be going for VISA interview in South Africa - hence the following links point to information specific to that country.
US Embassy, South Africa - Non-Immigrant Visas - How to Apply
The Visa Information Service Center (VISC) - The U.S. Visa Service