How do i launch a beam-riding missile

As title says… how do i…

Assuming you’re talking about Semi Active Radar missiles in aircrafts, you need to first lock your target with your radar…
To do that, you may want to look up (and maybe change) the key in your controls (lock radar/IRST on target in weapon controls).
It is indicated to you with a yellow box surrounding your target on your screen (AB/RB, dunno about SB).
Then, simply prep your missile and fire just like you do a heat-seeking one.
Be sure to keep the lock until your missile hits!

Talking about the Vihkr rockets.

I figured it out. I have to turn on sight stabilization, then move the flashing box on top of the… red box with a circle in it, then i can launch