If you plan to study in the United States, you will most likely require a student visa, which is either a category "F" visa, or a cateogry "J" visa.
The visa is an information page placed in the passport that informs the border official (CBP) that the US Consulate approved you to enter the US in a specific visa category. The border official reviews your visa and other supporting documents (such as your letter of admission and financial statements) and provides final approval of your entry to the US. The offical does this by stamping your passport, a small white card called the I-94 and your Form I-20 (for F visas) or DS-2019 (for J visas). This activates your visa status and enables you to be a student at St. Ambrose.
Visit our Obtaining a Visa page to learn more about visas and the application process, which you begin after you are accepted.