Where & how are GS projects saved?

Hi, new user here so please excuse the simple question. I'm trying to find where my first GS project is saved on my Mac by default so I can make a backup copy of it for Dropbox. I just can't seem to find it, especially since I have no idea what I'm looking for!
Also, along the same line of questioning, I've downloaded a demo/example ".game" file but I'm not sure how to get it to open in GS. Where do I put these files?
Also, along the same line of questioning, I've downloaded a demo/example ".game" file but I'm not sure how to get it to open in GS. Where do I put these files?
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