I assume you have a command prompt that looks something like this...
C:\>
If you do you use the command "dir" to get a listing of the folder (generally referred to as a directory when in DOS) contents.
The command to change directory is cd. So you would type
cd Rockbox
to go into the Rockbox directory.
cd .. (they are two full stops)
will take you up one level.
Hope that helps.
h