First you make a layout that will act as a main page. Normally speaking you don't put any fields on it, just images and text to act as buttons. Every button has a Go To Layout action. Then maybe it's best to put a Go To Layout button on every layout that takes you back to the menu.
Then Go to "File" - "File Options"
And select "Switch To Layout" and then "Specify"
Here you select the layout you want to go to every time you open the file.