[6BL Bird-Dog]

I don`t know the what MCU stands for but they can be inserted onto the mission builder and can be attached to aircraft objects etc .
The simplest trigger type is the waypoint but there are also many other types ,eg,timers & zone proximty triggers.
These can be interlinked with other types of MCU ,eg Commands or Translators so depending on how you set them up a whole sequence of events can happen when the trigger is activated.
A simple example would be a player flying within a set distance of a target would trigger a flight of enemy aircraft to take off from a nearby airbase to intercept.
The Attached screenie shows some of the MCU on the right of the screen.
I have only just started playing around with the mission builder but there are many useful videos up on youtube on how operate it made by members of the Rise of Flight Community.