Some questions about spawning triggers

[hypno toad 0]

No, I do not mean spawning the triggers themselves, I mean make trigger for spawning units

I am trying to set up a mission where groups of zombies spawn when somebody enters a certain area/trigger. And the zombies disappear when the players leave it.

Can anybody help me out?

[hypno toad 0]

Anybody?

[fasad 1]

Zombies are not a native part of ArmA, they are addon/script dependent. Check the documentation that comes with whichever zombies you intend to use.

As for the trigger, use a repeating side present trigger, with appropriate script code in the onAct and onDeact lines (as required by your zombie script).