1) Download file and unzip if it is zipped so that you get file with .scm extension.
2) Inside GIMP program, go to Edit -> Preferences -> Folders -> Scripts and see the folder/path listed.
3) Copy/Move the .scm file from step 1 to one of one of those folders.
4) Restart GIMP (or inside GIMP, go to Filters -> Script-Fu -> Refresh Scripts)
5) And now script is active for use.
For example, on my Windows 10, my Folders -> Scripts listed
C:\Users\Tin Tran\.gimp-2.8\scripts
C:\Program Files\GIMP 2\share\gimp\2.0\scripts
so I just save my .scm files to C:\Users\Tin Tran\.gimp-2.8\scripts
