There are several schools out there that offer these programs. You take the test either at one of the schools testing locations or one of the RECs. You MUST take a test to get your ticker.
I personally do not like the online courses because it is very difficult to learn plotting and Rules of the Road (lights, day-shapes, steering rules etc.) without the ability to ask questions from an instructor as well as discussion with other students. Furthermore, there are less distractions when you have to sit in a classroom versus being at home where phone calls and other distractions can affect your focus.
That being said--the advantage is you can do the course work at your own schedule.
I have a license and I have been a USCG license instructor. I think students do better when they are in the classroom versus in front of the computer. The computer should be used as a supplemental tool and not as the primary means of a lecture.
This license is a professional license, would you want your surgeon to take online courses or have actual experience with a scalpel?