The built-in Ubuntu remote desktop (or desktop sharing) is only really useful if you have external ssh Internet access to the system. For systems with no external access, teamviewer can be used to access the system. Teamviewer is also generally needed for GCWerks support, to allow temporary remote access.
Sharing the desktop
To share the desktop (the monitor on the PC), enable desktop sharing as shown below. The configuration is called either desktop sharing or remote desktop.
The desktop can later be accessed with a vncviewer through ssh (be sure the firewall is on). The user must be logged in for this desktop sharing to work.
To allow access from a vncviewer under Ubuntu 14.04, type the following in a terminal window on the desktop being shared:
gsettings set org.gnome.Vino require-encryption false