The default installation of Pop! OS uses the Gnome 3 desktop environment which has no traditional dock like Ubuntu, macOS or Windows. If you press the [Super] key, a dock-like element is visible on the left, but only in this overview mode…

Using the Dash to Dock plugin for Gnome, you can have a pretty customisable dock if you need it.

All you have to do is visit the following url in Firefox:
https://extensions.gnome.org/extension/307/dash-to-dock/

Yes, this will only work in Firefox and you will need to install the GNOME Shell integration plugin first. After installing the plugin, reload the page and click the on/off switch to install Dash to Dock.

To turn the plugin on, use Gnome Tweaks, where you’ll find the Dash to Dock plugin in the Extensions tab. To install Gnome Tweaks, copy this into the terminal:

sudo apt-get install gnome-tweaks

You might have to reload Gnome first if you don’t see the plugin in Gnome Tweaks. You can do this by either logging out and in, restarting your computer or by pressing Alt+F2 and typing r and pressing enter.