G1 is at 16+, and is written. Need to drive with someone who has had a license for 4 years. No highway driving.**
G2 is a driving test, but only covers in town and parking basically. Can now drive on your own, and can now start driving on highways.
G (full license) is the second driven test, and it includes highway driving...so being able to merge properly on and off ramps and such.
If you want to get a motorcycle license...it is the same thing. Written and one driven test (possibly two...not 100% sure on that).
At each stage, you have restrictions, that get lightened as you go.
**By highway driving, I mean that you are not allowed on certain highways, and they are all 3 or more lane highways. You can drive on a 2 lane highway, as long as it is not one of the listed ones.