Extract the zip into a sub-folder, for example public_html/groups, and open https://your-domain/groups/. The installer detects the folder and sets the site address for you.
The .htaccess file in the root of the script sends every request to the public folder and blocks direct access to private folders, so you do not need to change the document root. If your host lets you choose the document root, pointing it at wagroups/public is the cleaner setup and also works.
The license covers the domain, so a sub-folder of the same domain uses the same license.