Generally, a citizen of a foreign country who wishes to enter the United States must first obtain a visa, either a nonimmigrant visa for a temporary stay, or an immigrant visa for permanent residence.
Visitor visas are nonimmigrant visas for persons who want to enter the United States temporarily for business (visa category B-1), for tourism (visa category B-2), or for a combination of both purposes (B-1/B-2).
Here are some examples of activities permitted with a visitor visa:
Visit with friends or relatives
Participation in social events hosted by fraternal, social, or service organizations
Participation by amateurs in musical, sports, or similar events or contests, if not being paid for participating
Enrollment in a short recreational course of study, not for credit toward a degree (for example, a two-day cooking class while on vacation)