As a foreign national, you will need to obtain a temporary immigration visa from the United States in order to be allowed entry into the country. The most common type of visa for students attending the University of Colorado Boulder is the F-1 student visa.
In order to acquire either of these visas, it is necessary to have an appointment with a visa official at the nearest U.S. Embassy or Consulate. You are required to pay the U.S. government SEVIS fee to make this appointment, and to bring your application materials, admission offer, passport and immigration documents issued by the university (described below) to the appointment. It is best to try to receive this visa as soon as possible after your admission.
More detailed instructions on how to apply for your visa will be sent to you upon admission to CU Boulder, along with your admission offer.