Suppose that you wanted to launch Terminal, the command line utility located deep within the Applications Folder.  By the way, it's located at:

Macintosh HD > Applications > Utilities > Terminal

To open Terminal via Spotlight simply launch Spotlight then begin typing Terminal.  As with any Spotlight search, Spotlight intelligently adjusts what it has located based on the characters you enter.  You won't even have to completely type the string 'Terminal'.  For example, Spotlight has already identified Terminal after typing 'Termi'.

If you completely typed 'Terminal', you'd see a much more specific and narrowed search:

In both cases notice that Spotlight has highlighted a row called Top Hit with Terminal shown as the value.  To launch Terminal you could hit enter or use your mouse to click on the Top Hit row (you could also click on the Applications row).

You now have a quick and easy way to launch Mac OS X applications.  This can all be done via the keyboard without any use of a mouse of track pad.