Fortnite is distributed as three different game modes, using the same engine; each has similar graphics, art assets, and game mechanics.
Fortnite: Save the World is a player-versus-environment cooperative game, with four players collaborating towards a common objective on various missions. The game is set after a fluke storm appears across Earth, causing 98% of the population to disappear, and the survivors to be attacked by zombie-like “husks”. The players take the role of commanders of home base shelters, collecting resources, saving survivors, and defending equipment that helps to either collect data on the storm or to push back the storm. From missions, players are awarded a number of in-game items, which include hero characters, weapon and trap schematics, and survivors, all of which can be leveled up through gained experience to improve their attributes.
Fortnite Battle Royale is a player-versus-player game for up to 100 players, allowing one to play alone, in a duo, or in a squad (usually consisting of three or four players). Weaponless players airdrop from a “Battle Bus” that crosses the game’s map. When they land, they must scavenge for weapons, items, resources, and even vehicles while trying to stay alive and to attack and eliminate other players. Over the course of a round, the safe area of the map shrinks down in size due to an incoming toxic storm; players outside that threshold take damage and can be eliminated if they fail to quickly evacuate. This forces remaining players into tighter spaces and encourages player encounters. The last player, duo, or squad remaining is the winner.
Fortnite Creative is a sandbox game mode, similar to Minecraft in that players are given complete freedom to spawn everything that is within the game on an island, and can create games such as battle arenas, race courses, platforming challenges, and more.
Source: Wikipedia