Normally to find out what's in a file, I'll check with http://www.wotsit.org where all sorts of file formats are listed.

But .cfg is such a generic file type that you're on your own. A text file is a good guess, try opening it with Notepad. If it's binary, you can look inside with a Hex Editor, but it will be up to you to decide what it is you're looking at.

Dennis