If you wish to attend a university or other academic institution in the United States, secondary school, college or university you will require an F-1 visa. You will need this student visa to travel, for the most up to date information visit https://uk.usembassy.gov/visas/study-exchange/
This will involve a visit to the American Embassy for an interview at a pre arranged appointment.
Non-immigrant visas are processed at the U.S. Embassy in London or the Consulate General in Belfast. If you are in the United Kingdom, you may schedule an appointment to apply for a visa at either post regardless of your nationality or status in the United Kingdom.
Should friends or family members want to come and visit you they will require an E.S.T.A (officially known as the Electronic System for Travel Authorisation) Applications can be made here.