Super Smash Bros. is a four-player almost-fighting-game where your goal is to knock enemies out of the screen. The more damage an enemy has taken, the farther they'll go. You generally can't defeat an enemy just by doing damage to them. You'll have to land a powerful blow to send them flying and earn a KO.
If you get sent flying, you can use double and triple jumps to try to make your way back to the arena. There are different modes, such as stock battles, timed matches, and team battles. This guide will cover them all, as well as the various single player modes.