FCC Rules for Marine VHF and a handy Frequency Chart
When do you need a license? If your boat is over 20 meters (65 feet) long or you are “for hire” you need a license. If you are traveling outside the U.S. or it territorial waters you need a license. Inside the United States and her territorial waters on pleasure craft not for hire and less than 20 meters (65 feet) long you do not need a license to operated a VHF radio.
Everyone on any boat requires a license to operate single side-band radio (marine HF). If you want to operate your HF on amateur frequencies you need a HAM radio operator license.
Here is the official notice from the FCC website.
If you need a license, perhaps you are going offshore, you can apply through the same FCC website.
There are about 50 channels and each has it’s own special use. Channel 16 is for hailing/safety/distress calls. That’s easy enough, but what about the rest of them? I’ve never been able to memorize them so I made a handy chart to keep by my radio. You can print it out, laminate it and hang it up at your nav station.