To be more specific:
- To get more Wood and Metal bring back everything you find in the world including weapons and armor.
- You can move all junk you find into a workshop at a settlement with one key press.
- Items placed in any settlement workshop can be accessed by all other workstations in the SAME settlement.
- If you have a Charisma of 6 you can get local leader and link your settlements.
- If you choose one central settlement you can make a link out to all the other settlements and then you can drop all stuff in the main settlement and all others will have access to it.
So if you take and drop all your "Junk" and weapons and armor onto a main base all the links will get it, but it can also not work depending on where you drop them.
Say Sanctuary is Settlement A, RR Station is B, and Diamond City is C, if you have Links from A -> B and A -> C stuff dropped off in A will be useable by A, B, and C. But if you drop stuff in B only A and B will be able to use it. (I could be wrong but I think it only shares between the cities that are linked and not through multiple links.