Installing GUI and VNC on Ubuntu Server

1- Install GUI for Ubuntu Server

After being installed, Linux Servers have no user interface. In the post, I will show you the way to install XFCE4, this is a lightweight graphical user interface but it is friendly to the majority of users.
Note: In case I use PuTTY to connect it to Unbuntu Server and execute commands to install XFCE4. You can execute direct commands on Ubuntu Server.
You can see more about PuTTY here:
Open PuTTY and connect to Ubuntu Server.
We have direct XFCE installing packages from Unbuntu's Software Repositories.
Run command:

sudo apt-get update
Next, running the command to install XFCE:

sudo apt-get install xfce4 xfce4-goodies tightvncserver
After being installed, XFCE will takes about 523MB, pressing Enter to confirm the installing
XFCE is being installed:
XFCE has been installed successfully.

2- Install VNC Server

Next, you need to run VNC Server on Ubuntu. Then, installing VNC Client to your computer to be able to talk with VNC-Server. At that time, you can work with Ubuntu Server having the XFCE graphical user interface.
Running command:

Enter password (a maximum length of  8 characters):
An object "VNC Server" is running and it is waiting for the client which connects to. The object is listening at the exended port :1
You can create another object "VNC Server", it will listening to at the extended port :2
Using the command below to kill one object "VNC Server" having the extendes port :2.

vncserver -kill :2

3- Install VNC Viewer (VNC Client)

VNC Viewer is a VNC Client which supports you in connect to VNC Server and controll Ubuntu Server.
Firstly, you need to download VNC-Viewer.
The result of download:
VNC-Viewer can run directly without installing.
Create a connection to VNC Server:
Connect to VNC-Server via the extended port :1
A connection is created, double-click on it to access to Ubuntu Server.
Now you have connected to Ubuntu Server, and you can use graphical user interface to work with it.