You can lock the system immediately by simply clicking "Lock Now".
Setup the schedule options to let Desktop Lock lock the system at the hours you specified.
Virtual desktop is similar to real Windows desktop. It lists allowed programs on its desktop, and contains task bar, start menu.
In Welcome screen, you can choose a profile to login to the virtual desktop the profile contained. Virtual Screen supports multiple profiles, it means you can create several virtual desktops.
A profile contains a virtual desktop (with allowed programs, separate password and other settings).