The GNOME file manager is based on the GNU Midnight Commander, and can be invoked from the panel's main menu or by typing at the shell:
$ gmc &
The file manager allows users to navigate their directories and the rest of the filesystem with an easy graphical point and click interface. GNOME Midnight Commander adds even more functionality through its notion of Virtual File Systems (VFS): these are abstractions which allow you to navigate files that are not on your file system as if they were. Examples of virtual filesystems are the ftp filesystem and the tar filesystem: files can be accessed by anonymous ftp or by extraction from a tar file, and Midnight Commander treats them in the same way as local files.
Midnight Commander is powerful and vast, and it has its own manual (available by typing man mc) so I will not give more detail now.