you are dropped on a quite large island with your clothes or lack of them with 99 other players, you scavenge for everything, weapons, armor, ammo, other clothing, vehicles, etc. at intervals a circle is created that is the "play area" and then another circle constricts towards this, if the second circle passes you (seen on screen as like this big blue wall of energy) you start taking damage per second, as people die and time elapses the main circle constricts further and further (as does the damaging blue circle) until there is only one person alive. third/first person shooter is the combat, which is closer to ARMA than CoD in design.
oh, should note one thing that really works for the game, when you die, you can instantly run again, you don't have to wait out the "round" or anything