Hi,
first you should be aware that there cannot be a single definitive "start menu" on a linux system because there isn't a single desktop environment as integral part of the system like in windows, you can use whatever environment you like -- and each of them has its own concept of a start menu, which can be configured as you like.
There is nowadays some standardization going on, so if you use for example KDE, you will find most of your installed programs in its start menu.
Another idea in the debian distribution is the "menu" package, it handles configuring the menu of ANY installed desktop environment and/or window manager, so it contains a "debian" submenu with ALL installed packages. I assume this packages exists in Ubuntu, too.
And, finally -- learn to use a shell
All packages install their executables in /usr/bin (some essential packages in /bin, packages for the super-user in /usr/sbin or /sbin). Just look there