I know Xcode can be hooked up to an SCM. But how would I set this up from scratch? How to check out / commit files into that, after setting it up?
Once it is set up, several new menu items appear in the SCM menu. You can right-click over specific filenames and perform some SCM operations that way.
You can also right-click over "Groups & Files" and enable "SCM" there, which will show which files are new or modified.
I never used Xcode's SCM features for anything more than to see what files I've modified, a feature that only helped me find the code I was currently fixing. For all the updates & commits, I would use the command line, but that's a personal preference. I'm a long-time command-line CVS and SVN user. It is faster for me on the command line.