In the United States, the Federal Communications Commission (FCC) regulates amateur radio communications. The FCC has established a number of different license classes, each of which has different privileges. The most popular license class for ham radio operators is the General Class license, which allows access to all amateur radio frequencies. To obtain a General Class license, you must pass an exam that covers topics such as radio theory, regulations, and operating procedures.
If you are interested in getting a ham radio license, you can find more information on the FCC website. You can also find ham radio clubs in most communities that offer training and support to new hams.