You are in a post-apocalyptic world and have to defeat the opponents and try to get through the levels. Take heed of your ammo and enemies.You can look around with your mouse and walk with W, S, A, D keys, open the doors with "space bar" .
Try to avoid dangerous zones. You can see some of them but sometimes you need to use your detector ('Q' key)
Usually your final destination is marked by an arrow. Items you need to pick up or use before leaving level are marked by circles.