The B-Visa is generally known as the visitor visa. In general, if you want to visit and not live or permanently stay in the United States you must first obtain a visitor visa. Travelers from certain countries may be exempt from this requirement if they fall under the Visa Waiver program.
There are two main categories for visitors, the B-1 visa/status or the B-2 visa/status. The specific requirements can be found here B-1 visa/status & B-2 visa/status.