The first edition of Super Smash Brothers, Super Smash Bros. for the Nintendo 64. This game only had twelve characters. The eight unlocked from the start are listed in order, then the other four unlockable are listed unordered.
Like all Super Smash Bros games, you can determine the rules of each game. Up to four players can play in a versus mode. You can choose either a time mode, determining the winner by how many times each player has died and the percentages of each player by the time limit; or stock, which determines the winner by who kills the opposite player a determined amount of times: usually 4.
There is also a single player adventure mode where you fight a predetermined order of opponents increasing in difficulty until finally a boss fight at the end. There are also training and minigames for players to learn new techniques, practice characters, learn movesets, and have fun.
The stages on Super Smash Bros are Peach's Castle, Congo Jungle, Hyrule Castle, Planet Zebes, Yoshi's Island, Dream Land, Sector Z, and Saffron City, with an unlockable stage: Mushroom Kingdom. There are also other stages only playable on single player modes, as well as some stages that are completely unplayable, only playable with cheats.
Unfortunately, Super Smash Bros at this time wasn't widely renounced as a competitive game, and so no largely publicized competitions were held until Melee a few years later. Super Smash Bros for the Nintendo 64 now has very rarely competitions including but not limited to: stock competitions and combo competitions.