You must first check to see if you have any VNC hosts started - and end their sessions. If you're not certain how to end your sessions you can follow the instruction here to stop them. If you've never created a VNC server before you won't have to worry about any existing sessions. 

You're now ready to restart your VNC session. If you had already started a session and had to kill it, you may not be given the same session id as you had previously. Always read the information to see what your new VNC Unix desktop session will be.

To begin, you must first set a vnc password.

<umnetid@deneb:194>$ vncpasswd

Using password file /home/u7/umnetid/.vnc/passwd

VNC directory /home/u7/umnetid/.vnc does not exist, creating.

Password:

Verify:  

Would you like to enter a view-only password (y/n)? n

Next, start the vnc server

<umnetid@deneb:195>$ vncserver

New 'deneb:4 (umnetid)' desktop is deneb:4

Creating default startup script /home/u7/umnetid/.vnc/xstartup

Starting applications specified in /home/u7/umnetid/.vnc/xstartup

Log file is /home/u7/umnetid/.vnc/deneb:4.log

You are now ready to connect to Unix using VNC!