It shows some simple menus from Omen and Postal and the actual code written for it, in a step by step manner. Be sure to read all the replies as there are some extra tricks you can do that I've posted as replies.
Postal goes a step further though, by letting each Postal standalone submodule define their own menu function (its own module submenu) which the core addon calls. I didn't bother explaining this in the guide but you might be interested in the code. It's quite simple. A number of Postal's submenus goes 3 layers deep and are all generated dynamically (lists of sorted friend names, etc).