First, use no save mode because it only works there. Second, when the Sega logo is shown tap the letters. Do not slide it or it will not work. Third, after the jingle stops tap the screen with your two fingers. There you now have the debug screen.
You need 50 Rings and then to jump into the Big Ring at the end to play a special stage. Try to get the Chaos Emerald. Try to get all 6 and finish the game. If you don't collect any emeralds, at the End, Dr.Eggman will stand on to of the words "Try Again" juggling the Chaos Emeralds. If you collect some Emeralds, Eggman will juggle just the one you didn't collect. If you collect all the Emeralds, he'll trounce the word "End" repeatedly. It's funny. And it's better than the Emerald Juggling.
if you really need to beat a boss, just make sure that you have at least 1 coin. as long as you have one, you can not lose a guy, which gives you the advantage against the bosses.
In this level you have no rings so be careful.
Stand between 2 pillars. If robotnik appears, then smash him. The lasers will now come. Stand in the middle and jump when they are near you. Repeat this until he is defeated, then run after him. The next bit does not matter.
Smash into robotnik's ship and complete the game!