You must try and survive as the last standing combatant against the hundreds of other players online. Use the WASD keys to move around the map and use the left click mouse button to shoot. You must interact with various objects in the world to pick up supplies to survive.
Look for weapons and food and try to eliminate as many other players as possible. You also have to watch out for the poisonous gas that steadily closes in on the map and makes the playable area smaller - if you get caught in the gas you will eventually die. Good luck!