When you start the system you are presented with one of two login screens: a text login or a graphical login screen. If you are presented with a text screen then you should log in and execute the startx command to run the GNOME. If you are presented with a graphical login screen the you can select the GNOME as your environment and log in. At this point you should be in the GNOME, which is split into two parts:

The Desktop: This is actually the entire screen area. Pointers to frequently accessed files and applications can be located on the desktop for fast access. There are four such desktops by default that can be configured separately.

The Panel: The panel is the bar at the bottom of the screen (by default). This is used to launch applications, switch between desktops and lock the screen for security. In GNOME this is also used to display and switch between active applications (like the taskbar does in KDE).