If you use the fire-beam sexp the short answer is yes, but this should be seen as a good thing for you since you can control exactly when you want the beams to fire. If you want a beam to fire somewhat regularly, you can set the 'trigger count' (a small box in the events editor which holds a number) of the event to a number greater than 1. Set the trigger delay to the ammount of time you want to set between beam shots.
If you would prefer not to activate beams this way, you can let the computer(AI) take control of the beams by using the beam-free-all sexp. Once active, the computer will fire beams from the given ship at any hostile ship which is roughly 4,500m away depending on beam type. The wait time between AI controlled beam shots is dependent on the AI class and beam type set for the ship.
Cutscene sexps usually take some getting used to if you are new to FRED. Do you understand how to use the set-camera and camera movement sexps? You might want to just try making a fun dogfighting mission or similar just to get started.