US Tourist Visa

I have a Mexican friend that would like to visit the states. Can anyone tell me what he needs to do to apply for a visa. Thank you.

Here's the place to start.
http://mexico.usembassy.gov/visas/non-immigrant-visas.html

It will be a timely, costly, burdensome and humiliating experience. He can meet all the requirements and still be denied a visa with no reason given and no refund of the thousands of pesos it will cost. It is part of the long-broken USA immigration policy.