Hmm, 'triggers' is a bit ambiguous. Any condition->action group could be considered a trigger.
I'll take a stab at what I think you might refer to. In many games, the player walking over a certain spot might trigger an event, or some similar thing?
For example, a hidden trigger spot can be made by making a sprite to serve as the trigger point, setting it to be 'invisible on start', giving it a private variable 'triggered', then setting a couple of events like so:
+ player: player overlaps trigger
+ trigger: Value 'triggered' Equal to 0
-> trigger: Set 'triggered' to 1
-> (do stuff that only happens once, unless 'triggered' is set back to 0)
OR... for duration effects and such:
+ player: player overlaps trigger
+ trigger: Value 'triggered' Equal to 0
-> trigger: Set 'triggered' to 1
-> (do stuff that only happens right when triggered)
+ trigger: Value 'triggered' Equal to 1
-> (do stuff that keeps happening until you set 'triggered' back to 0 to reset the trigger, or perhaps 2 to make it a one-time only effect)
Anyway, if I'm way off the mark, you may want to explain in detail what you want to achieve.