explain triggers please

I want to make a TRIGGER, it is my first time so I'll try to be slow so you can see what I am hoping to do.
I have a plane it has a mesh object we'll call "engines" this mesh move 90 degrees. the engines actually have 2 motors it.The engine will provide verticle and forward thrust.
I want the engine to stay pointing downward most of the time.
If you press forward, "w", the engine should move to its forward thrust postion (90 degrees or the end of the animation cycle).

I have come to 2 possibilites
A) To have 4 "jetNozzels" nodes 2 for upward and the others for forward thrusts. Then the animation would move the mesh into the correct postion before thrusting.
OR
B)Link 2 jetNozzels to the engine mesh so it will provide a linear thrust from whatever position the engines are in.

each will need equivalent amt of particle emmitiers for jetNozzels

So there is my problem, I'm sure some of you also are doing something similar, only problem is I have NO CLUE where to start and/or if both ideas work. If someone would please show be HOW to do this, with code snippets, and where they are suppost to go. I will in turn write a tutorial Glorifing you and your work so others will have a nice referance from the community. SO PLEASE PLEASE PLEASE someone help explain triggers to me.
Thank You Anthony Rosenbaum