Many Sonic games require you to use your keyboard. This one allows you to have fun with your mouse. Specifically, you will guide Sonic through the air by clicking your mouse.
It doesn't matter where you click on the screen. What matters is how long you hold down your mouse button. The longer you hold, the higher Sonic will fly. After you release, Sonic will begin moving towards the bottom of the screen. Allowing him to go all the way to the bottom will end the game.
The reason this game is challenging is because you have to control Sonic's movements to help him collect golden rings without crashing into the ground, nailing the ceiling or hitting an obstacle.