Choose File → New VM… (or the New VM… button in the Virtual Machines window). Only the name is required; the defaults are 2 CPUs, 2048 MB of memory and a 20 GB disk. The very first VM downloads the Debian base image (~3 GB) once — later VMs clone it and boot in seconds. VMs persist: stopping one keeps its disk, starting boots it again, deleting destroys the disk too.
A node without a hypervisor — a NAS, a container without /dev/kvm — runs the desktop without VMs: the list stays empty and says why, About This Computer shows the same reason, and everything else works as usual.
Right-click a running VM and choose btop to open its process monitor in an 80×24 terminal window. It runs the VM's installed btop over SSH; press q to quit and close the window. A failed launch leaves its error visible.
Double-click a VM in the list to open its window. The tabs:
0.0.0.0 (not 127.0.0.1) to show up here or be exposable.