how to download raw files

Raw files are just files - but to use them, you may need a particular version of macOS or third-party application.

Photos uses a Raw compatibility library built into macOS. Your signature indicates that you are running 10.11 (El Capitan).

Digital camera RAW formats supported by OS X El Capitan - Apple Support

They're just files. If you download them they'll go into the Downloads folder unless you've changed the default location.

Once downloaded you can put them anywhere you want that you have access to.