How to start vnc server on linux

[root@vis1 Oracle_binaries]# service vncserver start
Starting VNC server: no displays configured [ OK ]
[root@vis1 Oracle_binaries]# vncpasswd
Password:
Verify:
[root@vis1 Oracle_binaries]# vncserver

xauth: creating new authority file /root/.Xauthority

New 'vis1.nrgc.co.za:1 (root)' desktop is vis1.nrgc.co.za:1

Creating default startup script /root/.vnc/xstartup
Starting applications specified in /root/.vnc/xstartup
Log file is /root/.vnc/vis1.nrgc.co.za:1.log