PUBG aka  Player Unknowns Battle Grounds  is a  Battle Royale  game. The way it works is that there are 100 people playing free for all. You have a minute before the game to adjust your tactic. Then you get picked up by a plane and you get to decide where on the map you want to land. 

Landing on the ground you have literally nothing. Weapons, shields, med kits and everything else can be found on the ground and in nearby houses. The next couple of minutes players loot the houses and try to find the best possible gear while killing enemies and trying not to die. 

The best thing you can do is to land on a car and use it to travel to other locations faster. It's much more efficient to loot  with a car, as it's faster than walking. 

After 2 minutes the storm starts creeping in. There will be a safe zone on the map and if you don't get inside on time, you will slowly but surely start losing HP until you die.

The zone starts shrinking a little bit again after a couple of minutes and this process repeats  until there is no place on the map that is safe, or until there is only one player left.

Last man standing wins!