Patron and Apprentice
 

OK,

Very basic question, but I can find like NO documentation.

I have a Patron subscription and have a friend who just purchases an Apprentice subscription. How do I link these up so he can use my content?

You need to create a campaign and once the friend has joined, they'll have access to all the resources you've shared with the campaign.

And the PC(s) they create need to be owned by the GM. They can be player-controlled but they have to be GM-owned to participate in content sharing.