By default Ubuntu 12.04/12.10 comes along with the Unity shell interface. Unity is an interface for the GNOME desktop environment developed by Canonical Ltd. for its Ubuntu operating system. Unity debuted in the net-book edition of Ubuntu 10.10. In my experience many users - especially the ones coming from a Windows environment - find it rather difficult to get used to Unity.
If so, there is a very easy way to switch to the GNOME Classic shell which was used in Ubuntu 10.04 and which is quite similar to a classical Windows environment, having a start menu to launch applications and a windows bar to switch between running applications. The tutorial video below shows you how you can switch back to GNOME Classic in Ubuntu 12.04/12.10 and how you can combine GNOME Classic with the Unity launcher bar to get the best of both worlds.
To install GNOME, open the Ubuntu Software Center, search for "gnome-panel" and install the "Launcher and docking facility for GNOME". After the installation you have to log off, to switch to "Gnome Classic" with the button beside your name (see the following picture) and to re-login.