How to indicate the network to Google

I understand that each site gets its own code and how you’d set that up in Google. But I don’t understand how to differentiate the network from the main site. There isn’t a separate network sign-up or anything like that as these are really just separate sites that share some pages that won’t change much (done as theme templates).

In this case how would I distinguish the network from the main site when I set up analytics in Google?