There are two types of desktops:
Temporary: As its name indicates, it is a "temporary" desktop, that means that once a desktop is started, everything that has been saved or downloaded will be lost when it is closed.
Persistent: It is a desktop that is not deleted, when it is turned off, the information or programs that have been installed will not be lost.
To create a desktop, click the button
The fields are filled in, a template is selected and if you do not want to configure the advanced options of the desktop, press the button
You can change the desktop settings in the "Advanced Options" section.
Here you can select the viewers you want to use on that desktop, edit your hardware, add a GPU (if you have one), add isos and change your photo.