Ubuntu Server has no GUI, but you can install it additionally. Simply login with the user you created during installation and install the Desktop.
Install desktop Environment
First you nee to make sure you have enabled Universe and multiverse repositories in /etc/apt/sources.list file once you have enable you need to use the following command to install GUI.
sudo apt-get update sudo apt-get install ubuntu-desktop
The above command will install GNOME desktop
If you wan to install a graphical desktop manager without some of the desktop addons like Evolution and OpenOffice, but continue to use the server flavor kernel use the following command
sudo aptitude install --without-recommends ubuntu-desktop
If you want to install light weight desktop install xfce using the following command
sudo apt-get install xubuntu-desktop
If you want to install KDE desktop use the following command
sudo apt-get install kubuntu-desktop