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

Tutorials Completed (5 points): Complete the tutorial for each character.
First Blood (5 points): Try to be the first one that kills an enemy in challenge mode.
Ability First Kill (5 points): perform a kill using your ability for the first time in challenge mode.
Challenges Master (10 points): Win Death Match without being killed in a challenge.
Ability Master (10 points): Perform 10 frags in a row with only your abilities in challenge mode.
BlackOp Campaign Completed (20 points): Complete all challenges in the BlackOp Campaign.
Bishop Campaign Completed (20 points): Complete all challenges in the Bishop Campaign.
Guardian Campaign Completed (20 points): Complete all challenges in the Guardian Campaign.
ArenaMaster (20 points): Perform 5 kills without being killed in a ranked match.
Slayer (20 points): Get 100 kills in Xbox LIVE ranked match.
All Rewards Unlocked (30 points): Unlock all rewards.
Marathon (35 points): Score 1,000,000 points.