"Cover kills 0/3" is an optional mission objective in Sequence 3 / Memory 01: Graduation
Walkthrough
From the starting point in this mission, perform a Leap of Faith into the hay cart. Drop into Sneak mode and slip past the tents then take cover against the crates ahead Head over to the North, taking cover behind the crates and barrels there. There is a guard right by you at present. Just take a moment to ensure the other 2 guards aren't look then assassinate this guard.
For the second assassination, head back over to the hay cart. From there climb over the nearby fence and land down among the tents beyond it. Creep up to the crates that border the fencing. Go to the join between the crates and wait for the opportunity to assassinate the Guard by the Alarm Bell. Just be sure that the patrolling Guard isn't looking toward you.
Wait for the patrolling Guard now. Stay in the same position until he passes you by or is looking at the crates to the Northwest. Slip over to the second pillar on the Western side of the building. Just wait for the guard to come to you after that.
