I am a newbie learning the iOS.
Can someone please explain what is the purpose of the xcscheme file?
In terms of version control, you don't have to worry about xcscheme (or anything within and under the xcuserdata folders of an .xcodeproj).
What's inside the xcscheme file? These are the actions and configurations that happen when you build, run, test, profile, etc. These can be changed from Xcode user to user, which makes it friendly for using on multi-developer projects.
These are the same items you see within Xcode when you click on the "Edit Scheme" popup menu choice: