Listening to radio signals on frequencies assigned to amateur radio operation is legal for anyone, however, if you want to transmit on these frequencies, you must be licensed.
The FCC (Federal Communications Commission) currently issues licenses for three different operator classes: Technician, General, and Amateur Extra. The following is a description of each class as quoted from the FCC website:
The privileges of a Technician Class operator license include operating an amateur station that may transmit on channels in any of 17 frequency bands above 50 MHz with up to 1,500 watts of power. To pass the Technician Class examination, at least 26 questions from a 35 question written examination must be answered correctly. Technician Class licensees also have privileges in four amateur service bands in the HF range (3-30 MHz) (Refer to Section 97.301(e)).
The General Class operator license authorizes privileges in all 27 amateur service bands. Upon accreditation by a Volunteer-Examiner Coordinator (VEC), an individual can help administer certain examinations. In addition to the above written examination, the requirement for a General Class operator license includes a 35 question written examination for which 26 correctly answered questions is the minimum passing score.
The privileges of an Amateur Extra Class operator license include additional spectrum in the HF bands. In addition to the two above written examinations, the requirement for an Amateur Extra Class operator license includes answering correctly at least 37 questions on a 50 question written examination.
In order to get your amateur radio license, you must study for the required exam. Exams for the FCC licenses are administered by Voluneer Examiners (VE's). The Sandhills Amateur Radio Club has a group of VE's that can administer exams. Usually, this would take place at the monthly club meeting. If you're interested in testing, Contact Jim, AC0E (firstname.lastname@example.org).
For more information on studying for exams and getting licensed we've found the following write-up by John Goerzen, KRØL:
Getting Started With Amateur Radio
The Amateur Radio Relay League (ARRL), which is main organization which exists to advance amateur radio, also has multiple pages on getting licensed:
Page updated September 10, 2018