Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

Star Pupil (5 points): Complete all lessons in the tutorial.
First Blood (5 points): Complete the first challenge mission, "Dead Meat".
Victor (20 points): Complete all 13 main path challenge missions.
Superior Commander (50 points): Complete all 13 main path challenge missions under par time.
Future Leader (20 points): Complete all 50 challenge missions.
King Of The World (50 points): Complete all 50 challenge missions under par time.
Battle Tested (10 points): Complete any 10 challenge missions.
Battle Hardened (20 points): Complete any 25 challenge missions.

Additionally, there are four secret achievements:

Secret achievement (5 points): Unknown.
Secret achievement (5 points): Unknown.
Secret achievement (5 points): Unknown.
Secret achievement (5 points): Unknown.