How do I shoot when controlling the turret of a UAV?

I'm in a point in the Single-Player Campaign mission where I need to control a UAV and take out a target. I have successfully taken control of the UAV turrets, but when I press Mouse 1 (Fire), a red star appears on my screen, and clicking Mouse 1 again removes the star.

Can someone give me a detailed explanation on how to use the UAV in ArmA 3? Most importantly, how can I fire my UAV turret at an enemy?

(Please explain this as you would a child, as this is the first time I have ever played an ArmA game.)

You probably already know this, but for future reference... the UAV you have doesn't have any guns, just a laser pointer. Lase your target and the other team will start firing at them. If you turn on infrared you can actually see the laser dot.

I was banging my head with this as well, but you need to hit 3 for missiles and 4 for laser. You will see it change in the top right.