I setup a supply line but I dont see shared items?

I setup a supply line from Tenpines Bluff to Red Rocket Station and Sanctuary, but I dont see the shared items in the workstation? I have 50 Concrete in Sanctuary but can't see it in the Tenpines or Red Rocket station.

Can someone explain this to me?

Also how do I find the settler to delete the supply line?

As far as I know. I believe that you'll just use the materials from another settlement so long as they're linked. So if you're in Sanctuary Hills and you wanna build say, a bench which requires 5 wood and 1 steel, in Tenpines Bluff it'll just take the wood and steel out of Sanctuary's workshop inventory that is, if you don't already have the materials in Tenpines' inventory.

Junk material can be used to build stuff in another settlement with a supply line, but you can not directly see it or remove it from the workstation. Just like settlers in another settlement can 'use' food from linked settlement but you can not see it directly (they will not be hungry even if you don't have enough food in your settlement as long as you have a supply line to another settlement which has enough surplus food).