You cannot advance the story without completing this mission. All you have to do is kill someone though and you should be pretty good at that by now.
- Kill the target using a Sniper Rifle
This mission is another short and sweet one. Drive to the objective, take out your Sniper Rifle and dome the target. Mission complete.
Another request from Lester.
- Kill all targets as quickly as possible
A fast car and a sniper rifle are a must for this mission. You have a fair amount of time to complete these killings. As long as you complete them within the time limit, you will earn the gold medal. Just kill them from a distance with the sniper rifle except for the last one where you can just run him over.