Any idea how to have more than 2 workspaces on Ubuntu 18.04.1?
GNOME shell in Ubuntu 18.04 has a "dynamic workspaces" feature by default, which means there is no fixed number of workspaces.
Workspaces can be created on demand, and are automatically removed when empty.
There will always be an empty workspace below the workspaces you're using. Just open an application window in the second workspace, you should find a third workspace appearing (which is empty) and so on (check the official documentation for more info).
You can disable this feature and switch to fixed number of workspaces. First install (GNOME) Tweaks by running
sudo apt install gnome-tweaks
Then launch Tweaks and go to the "Workspaces" section. Select "Static Workspaces" instead of "Dynamic Workspaces" and set the "Number of Workspaces" to your preferred one, 4 for example.
Ubuntu 18.04 comes per default with workspaces.
To use workspaces, click Activities on above the vertical bar (dock) (or alternatively press Super), then move your mouse to the right of your screen to show the workspaces in used plus one empty one. Or switch using following short cuts.
You can also find a nice gnome-shell extension on following website.
Extension Homepage: https://github.com/passingthru67/workspaces-to-dock
To install visit this page and switch the slide on.