There are many different types of U.S. visas that allow you to work in the United States. Citizens of Canada and Mexico, for example, can apply for a TN/TD visa that allows them to work in the United States for a three year period. Other nationals can get an employer to petition their visa application to allow them to work in the United States.
Meanwhile, those on immigration visas can achieve lawful permanent resident status (i.e. a green card). A green card allows you to work in the United States.