How can you back up files of a computer game?

My computer is getting reformatted. How do I back up the data of the game?How can you back up files of a computer game?
Depends on which game. Usually game data is stored in .SAV files or an equivalent, but sometimes it's much more obscure. You could try copying those files to a different location, but that may not work either. I suggest you image your hard disk before you reformat it, just in case.