This is argubly the easiest achievement in the game. You can obtain this achievement in 2 ways as mentioned in the achievement description.
Either load up any campaign mission (this includes any prologue and epilogue campaign missions) or multiplayer map and finished the mission/match. Once your finished the achievement should just immediately unlock.
Note: Firefight doesn't work for this achievement as for some reason the game codes don't count it as a campaign mission or a multiplayer match, weird!