In the initialization field of the unit, put the following code:
this setPos [(this getPos) select 0, (this getPos) select 1, x]
Replace x with the height that you desire.
The laser designator is used to guide laser-guided bombs to a desired point of impact--generally enemy units. The laser designating unit must turn on the laser by pressing the fire button (usually, mouse button 1, a.k.a. the left mouse button) once while aiming at the desired target. Next, a unit with laser-guided bombs (with official units, only the A-10 (GBU) has laser-guided bombs) must target the laser as you would any other enemy vehicle. That is, use the Tab key to cycle through your targets until the laser is targeted, or else right click on the laser target on the radar. Finally, fly at an appropriate altitude and speed toward the laser, and drop one or more bombs at the right time. The bomb will travel to the laser, as long as it had enough altitude to reach the target.
Supposedly, Hellfires can also be used to target a laser, but I've never tried it.