7. Triggers
Triggers are used to start certain events on the map. They consist of a general flags area, an event area and an action area. The flags area just sets the name of the trigger, whether or not it should repeat and who owns the trigger. The events define when this event shall occur. Finally, the actions define what happens if the events are true.
Example: If time passed is 50 seconds then send some units to the player.
This is how the trigger editor looks like:
The trigger editor has documentation about every trigger. Please see the Tutorial to find out more.