PlayerUnknown's Battlegrounds is a 100 Players online PVP game. There is no offline mode or single player option. You are dropped off on an island with nothing and forced to scavenge for equipment and weapons. To win - you must be the last one standing.
From the official PUBG webpage:
Our BATTLE ROYALE game-mode will put up to 100 players on a remote island for a winner-takes-allshowdown where strategic gameplay is as important as shooting skills. Players will enter a last-man-standing battle where they try to locate weapons, vehicles and supplies in a graphically and tactically rich battleground that eventually forces players into a shrinking play zone as they engage in a tense and spectacular fight to the death.
Each game mode supports either first person only - or third person, with optional first person camera perspectives.