Access Applications directory in Terminal
In the Terminal you can type the absolute path...

cd /Applications


to access applications installed for all users.

If you want to access the root folder (named "Macintosh HD", in your case), it called / in Mac OS X (and other UNIX variants).

And cd, meaning change directory, is used to navigate.



Alternatively, you can use the shortcut &#x2318;+&#x21E7;+G in the Finder and type...

/Applications


You do not need to type out the whole name. Tab-completion automatically adds the last letters. You can invoke tab-completion by pressing &#x21E5; while typing /Applications.