There are two flap settings, Combat and Level (I think that is the labels). It will pop a text when you hit the flap button. Combat is for whenever you need more lift at slower speeds, like tight turns and landing. Level is for when you want maximum speed in straight flight.
Hitting the Trim will take a snapshot of whatever you have your controls set at, minus the throttle, and make that the settings of the controls when you let go of the stick. There doesn't seem to be any visual or audio indication when you hit the trim button. It would be nice if there were.
If you hit trim with wings level and the nose up it will stay that way when you let go of the stick. If you set it in a steep banked dive it will stay that way also.
The usual use is to set it when you are flying as perfectly level as possible. Easier said then done.