Understanding Share library

Hi
Help me understand this " Sharing a Itunes library " ( apparently you can have 4 people that can access the library )

Would I be able to download example : Music / Apps from my brothers Itunes account , if he stays in a dirrent location to me ?

I have my own account and also would like to share some of my apps etc with him.
I understand if we both stay in the same house , we can share in the house over the wifi , but we in different location.

Do I access his PC or his Itunes account ?

Please explain how it works

Thanks