add a new user to ubuntu :
sudo adduser newuser
add a new user to sudo group:
sudo adduser newuser sudo
#change userid to a new user
su newuser
newuser$ cd ~
newuser$ mkdir .vnc
newuser$ cd .vnc
newuser$ nano xstartup
#in this file you should write:
#!/bin/bash
xrdb $HOME/.Xresources
startxfce4 &
#to start vnc server from a new user:
newuser$ vncserver
#here we can see the port that was used for this user when the service started. This port should be #used for the further connections. (Port can be changed by restarting/starting vnc server):
newuser$ ps ax|grep vnc
#to kill the previous session of vnc in case if it is needed:
kill №proc vnc
#to start a new session from a new user:
vncserver