How do I

I want to know how you do to decrease life per second.

I can not. =//

Anybody know?

Every second subtract X from health variable

I can do it.

How do I continue counting with the game off?

Game with real time counting I guess. So you play the game at one time then close then at another time you open it the value change whether it is increased or decreased. Basically system need to calculate how long player left the game since his/her last visit.

I can do it.

How do I continue counting with the game off?

Are talking about having a real time game, like where you close the app and when you come back later resources have accumulated? I believe that usually requires storing data on a server.