A whole thread with an answer that can be solved with a manual...
Since your new, i suggest you go here:
http://esf-world.com/main.php?content=12xflashtut&lang=de
Remeber, it taks a little bit of ki to transform and if your trasnformed with a certain character and your ki depletes, you will go back to your normal form.
Each character has a certain Power Level to trasnform at, for example, trunks gets to go super saiyan at 1,000,000, while goku has to wait until he gets 1,750,000. This is all explained in the link above and more.