If you are a male in the United States, you should know about selective service requirements.
From http://www.sss.gov/:
Almost all male U.S. citizens, and male aliens living in the U.S., who are 18 through 25, are required to register with Selective Service. It’s important to know that even though he is registered, a man will not automatically be inducted into the military.
The law requires virtually all male U.S. citizens (regardless of where they live), and male immigrants residing in the U.S. (permanent resident aliens), to register within 30 days of their 18th birthday.
If you are required to do so, be sure to register.
The Citizens for Selective Service Education site (http://selectiveserviceinfo-ny.org/faqs-ssin.html#failure_to_register) states that:
Failure to register can result in five years in Federal prison and/or a $250,000 fine. There are also other civil penalties. Although no one has been prosecuted under this law for many years, proof of registration is required to obtain Federal aid for college or job training, as well as most Federal jobs. In New York State, as well as many other states, you must consent to be registered in order to obtain a driver’s license or learner’s permit.
You can register online, at a post office, by mail, by checking a box on the FAFSA, or sometimes at your high school.