Go to the planet the mission tells you to go to and kill enemies there. You'll start seeing them count up on the right side of your screen. Kills by Allies around you also will count this up. [b]I recommend you join this with a Strike[/b] as you'll encounter many enemies on the way to your goal and you're not just running around aimlessly. I've generally finished the full count by the end of the Strike mission, just fyi.