Generally, a citizen of a foreign country who wishes to enter the United States must first obtain a visa, either a nonimmigrant visa for temporary stay, or an immigrant visa for permanent residence. The visa allows a foreign citizen, to travel to the United States port-of entry and request permission of the U.S. immigration inspector to enter the U.S.
Nationals of certain countries may be eligible to visit the U.S. for up to 90 days without obtaining a visa. Please see section “The Visa Waiver Program and ESTA registration” for more information.
The B visitor visa allows for entry to the U.S. for a limited duration for business, with the B-1 visa, or pleasure, the B-2 visa. B visa visitors must have an unabandoned residence in a foreign country to which they intend to return at the expiration of authorized stay, demonstrate ties to the home country (i.e. bank account, job), have adequate finances to pay for travel to and from the U.S. and expense during the stay in the U.S. The visitor can only engage in “legitimate activities” relating to business or pleasure, so no employment or study.