Just control-click the button, and then choose Menus > the main menu from the target list. You can even select individual buttons on the main menu if you want to target a specific button.
You should checkout our DVDSP videos ... they are better than the APTS book, IMHO ... and I wrote the last half of it (so I probably shouldn't say such things ... oh well, i just tell it like it is)!!
The DVDSP VQP is also a great resource ... more task based so you can look up what you need and then do it. It is still for version 3, but quite frankly, not much has changed in DVDSP: