2 Ways, Adventure mode, or Sticker Album.
Adventure Mode-On the map screen, Press B to where it says Back to Map, Stickers, Save and Quit .Press on stickers. Now in the corner it will say what character you are one, and a trophy base. On the side there is a list of stickers, and on the bottom it will say the sticker name and how much and what it powers up. Scroll through the characters and put as many stickers as you can on each base, but make sure that it can go with that character. FOr example - Putting Electric Attacks +10 on Sonic wont do you any good because he doesnt use electric attacks, putting it on Pikachu would be best,
Sticker Album - Put stickers together to make a scene (picture) and take a snap shot.