How do virtual desktops and activities work?

I've been using Garuda in a virtual box on my PC and I love the customisation. However I am a little confused about the difference between a virtual desktop and an activity. While activities are easy to use and switch between I haven't seen the shortcut to switch to a different virtual desktop. I know this topic is very dumb but I am actually confused of the differences between the two.

Installing in virtual machines is not recommended as it might result in a bad experience!