If you seek to enter the united states temporarily for a specific purpose such as business, study, or pleasure, you are a non-immigrant and will probably have to apply for a temporary visa. Having an approved visa allows you to travel to the united states and request permission to enter the country. When you arrive at a u.s. port of entry, an official from u.s. customs and border protection (cbp) will grant or deny your admission to the untied states.