Answer:
I used to do trampolining for about 4 years so I hope I can help.
The basics:
To trampoline you need to bounce by bringing your legs up slightly and then releasing them down when you reach the floor of the trampoline.
I mean no offence it's not too difficult.
But then again if you are asking how to do moves like back somersaults and straightbacks etc, then I would advise to take up trampolining at a club. It would be dangerous to attemped any advanced or even simple move without support and training.
I would also advise you to make your question more detailed as I didn't know what aspects of "how to trampoline", you would want to know, so if this isn't what you wanted to know then delete it or change your question :D xx