Ubuntu Beginner Tutorials:

Complete Video Guide on How to Install GNOME 3 Shell Extensions on Ubuntu 18.04.1 LTS.

How to Install and Use GNOME Shell Extensions in Ubuntu.

Step:1 You have to install an add-on based on your preferred browser.

Step:2 After installing and enabling above addons, open terminal and run below commands in Ubuntu 18.04 :

sudo apt install chrome-gnome-shell

Step:3 Go to extensions.gnome.org via your choice of browser and search for any extension.

Step:4 On the extension page’s top right section click on the button to turn it on.

Step:5 In the confirmation dialog, click Install

Once installation completes, you are ready to go. You can see the extension in the works for you.