The process is different depending on what state you are in. In some southern states, you can get a license when you are 16 (or even 15 i think). The only state's I know for sure is NJ, because I went through the process there. These are the steps I did to earn a full license (I don't believe all of them are mandatory).
1. Take a 20ish hour defense drive class. It was all theory, no actual driving was done. <---I don't think this is mandatory.
2. Take and pass the written test, which is where questions like "If a school bus stops with its sign out, is it ok to pass it by driving slowly on the sidewalk?" appear. <---mandatory
3. Turn 16. <--mandatory
4. Drive for 6 hours with a certified instructor. It was in a special car where he had a brake on his side. <----pretty sure this is mandatory.
5. Get your learner's permit by going to the DMV with your instructor. This allows you to drive with anyone who has had a full license for 3 years and is 21 or over (usually a parent).
6. Wait six months or turn 17, whichever comes later (supposedly practicing during this time). <---mandatory
7. Go to the DMV and take/pass the practical test. This entails turning properly with signals, stopping, following speed limits, k-turns, u-turns, parking, parking on a hill, and parallel parking. If you fail, you have to wait 2 weeks before taking it again. If you fail 3 times consecutively, you must wait 6 months.*
8. Once you pass, you show the DMV people a bunch of identification (birth certificate, social security card, visa, school id, etc) and get your restricted license. This allows you to drive alone between 5 am and midnight. No more than one person outside of your immediate family may be in the car during this period.**
9. Wait 1 year.
10. Go to the DMV with proper ID and get your full license. No test of any kind is done here.
*I failed twice and passed on my third attempt. Parallel parking screwed me both times. I have yet to ever be in an accident or be pulled over and consider myself to be an excellent driver.
**I think this is the key step and why NJ's process is probably one of the best. Allowing only one friend/distracting person int he car with a new driver makes it possible for the driver to concentrate on driving properly. It also prevents kids from driving during a time where they will probably be more inclined to screw around.
And remember, when it comes to defensive driving, the best defense is a great offense.