How do I link my main menu to the page where the 2nd menu is on the 2nd site?

What I’m looking for is a menu system where it links to other pages that then have a different menu at the same place as the home primary menu but this new menu links to other pages.

I’m running Twentythirteen. I’ve now got the Multi Site. I’ve got the menu on the main site working fine but how do I link that menu to the next menu on the new site??