The trim controls the aircraft's going up or down.
So to make the aircraft go up you can:
1) Push the stick down and the aircraft points down.
2) Trim down and the aircraft points down.
And the opposite for "up"!
Now you may say, Why on earth have trim then if I can use the stick?
Well it is an essential and important extra to flying. if you are climbing to 4,000, for example after take-off, you are going to have to hold that stick for a real long time in that position and it is hard work. If you use trim you can release pressue onthe stick and the aircraft will climb. You can actually fly the aircraft in the air by the trim wheel. It can be used to fly straight (can be hard to do if you aren't used to it!) or used to ascend or descend.
Hope this helps.
Ben
