Ubuntu has a build-in utility which provides functionality for other users to access your desktop using the VNC Viewer utility.

Navigate to System–>Preferences–>Remote Desktop,you will see a window like this:


The two checkboxes under Sharing section need to be checked for remote desktop to be enabled.

The first checkbox in Security section means you must be at the computer to allow other users to access your desktop.If you want to access your own computer remotely,uncheck this box and check the third one.Enter a password behind second checkbox,and other users need this password to access your desktop.