A Few Questions......
How do u go back a directory in the terminal, such as you start in the users folder, so how would you get to the Macintosh HD?
How do you switch to another Hard Disk?
But to answer your questions to get you going:
To move up a directory, type "cd .." (without the quotes). There is also an alias set up "..", so if you type two periods, it will bring you up one directory.
To switch to another drive/partition type "cd /Volumes/Drivename", "Volumes", like everything else in the command line, is case sensitive and by "Drivename" I mean the name of the drive or partition you're trying to get to.