The gnome-shell extensions won't be usable until the gnome-shell
gets restarted. To do so, running the shell, press ALT+F2 and
type 'r'. That will restart the shell.

To enable or configure an extension, after restarting the shell, you
have to open a new gnome-tweak-tool instance. The new extensions
should appear in the extensions section.

Use the extension at your own risk.