You must typically have a visa if you are foreign citizen and wish to visit the United States. if you are visiting temporarily, you would obtain a nonimmigrant visa. if you want to reside permanently in the U.S. you will need an immigrant visa.
A visitor visa is a nonimmigrant visa for travelers who want to come to the U.S. on a temporary basis for business purposes (a B-1 visa), as tourists or for similar purposes (a B-2 visa), or both (B-1/B-2).
The following examples illustrate the kinds of activity permitted by visitor visas:
B-2 Tourist/Visit Visas
The following examples illustrate activities not permitted by visitor visas; they require other types of visa: