Do you mean terminal? Or possibly xterm?
When you turn on a properly-installed and supported Ubuntu machine, it should go to GRUB (the boot menu) and then to a screen that says Ubuntu with a bar moving back and forth and then loading, and then to a screen that says Ubuntu in the middle with a username/password login. This screen is brown/orange and has a themed background. If you're getting a black screen with text telling you to input your name and password, it isn't working right (that black screen is called the terminal, it is a command line interface that Unix/Linux machines use when they can't run a window manager or don't have one installed).
If you get the nice login screen, that means your X server (the program that manages use of your graphics hardware and screens) is working properly. If you get to the nice login screen, go down to the bottom, click Sessions, and choose Failsafe GNOME. GNOME is the default window manager in Ubuntu, it is the program that takes care of drawing menus, windows, backgrounds, and other on-screen elements. It requires the X server to handle the hardware for it. Failsafe GNOME boots up a GNOME session with minimal extra startup processes (kinda like Safe Mode, but not for the entire OS, just the user interface). If this doesn't work and you're at the terminal, you can try entering the command "startx". This will attempt to start the graphical user interface.
