Import/Download the extension and install it like every other extension.
Include the static TS (from extension) in the template record (your root TS or make an ext. template just for the page where you want the extension be displayed). The steps for the real beginners are:
Select your root/first page.
Click in the menu on the left side “Template” and choose “Edit whole record”.
Scroll down until you see the the same thing as in the screenshot shown.
Search for the “Slideshow (rgslideshow)” entry on the right side, click on it to get it on the left side.
Press “Save” and you are done.
Follow the chapters “Administration” & “Configuration” below.