What do I do after I mount an image?

[jn117]

I have an ISO file of a game I own that I'm trying to play without the CD. (Civilization 5).
I've tried multiple times to open the file with DAEMON, but each time it keeps having me install the game all over again.

How can I get it so that once I install I can play the game?

[Blazkowicz]

Game is using Steam, therefore you shouldn't have to insert the disk to play normally.