Step 1: go to the osu! download page and download the installer.
Step 2: go to your downloads folder by going to your file explorer and clicking downloads below Quick Access.
Step 3: double click the osu!install.exe and wait for a couple of seconds.
Step 4: make an osu! account.
Step 5: go to the Rafis skin download page and search for "Rafis 2018-03-26 HDDT" and then click on it to download it.
Step 6: log in to your osu! account on your browser if you haven't already.
Step 7: (optional) log in to your osu! account on the osu! game as well.
Step 8: go to your downloads folder again and double click the "Rafis 2018-03-26 HDDT.osk" file.