You do not grant additional resources to tickets. Tickets are put in a Department. Only those with access to the Department would be able to see and work the ticket. It might be helpful if you think of a Department like a bucket that only members of that department have access to. To have another Department work on it, the ticket would be transferred to another Department.
The build in exception to this is Teams. Teams can be comprised of Agents from multiple Departments. It's still a bucket to put ticket into though.
Referral access is for when you transfer a ticket to another bucket (team or department) and want to be able to see/read/follow the ticket as it travels through the workflow in another bucket.