Tried To Install Lilypond...

I apparently did get Lilypond to install from Synaptic as it is all green boxes for the pertinent files, but cannot find it anywhere in the menu. When I try searching for it, it just brings up the Lilypond website.

How do I access the program and more so- how do I get it into the main menu?

LilyPond is a text-based music engraver. You will need to read the manuals on how to use this software before going any further. There is no GUI for the menus to point to.
http://www.lilypond.org/manuals.html

If you want or need a GUI to handle the text editing look here:
http://www.lilypond.org/easier-editing.html