How to get an Ubuntu system that boots to the command line to start the GUI?

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http://askubuntu.com – As the title above, I am totally new to Linux. What I have now is a virtual hardisk with ubuntu and it started up as CLI. What I want to do is enable the graphic mode and able to switch it flexibly. So, I wanted to install ubuntu-desktop due to the fact that Ubuntu only started in terminal mode and I couldn't get startx command to run too. The startx command ended up by open a CLI with white screen. Right now, I ran "sudo apt-get install ubuntu-desktop" but I dun know how to enable it or activate it. Can anyone please kindly brief me about that? Between, my internet connection is bad, so th (HowTos)