Questions about VPN and hosts on different locations

Hello folks,
They say there are no stupid questions. I try NOT to pretend that I know, I am asking even that I may look like a fool.
With this aside,
I have set up a VPN server on Linode, everything went butter smooth.
Now, some questions arise:

If my computers are connecting to the VPN server, each one running the Wireguard aplication, where do I have to set up or modify that the computers talks with each other?

If my router runs the VPN or becomes the VPN server, the computers connecting to the router have to run the Wireguard client, or they are on the VPN connection because the router already runs the VPN?

And if different computers from different locations are connecting to the same VPN server, being on Linode or my router, how can they see each other and share files or a printer?

New to the whole VPN stuff, as I said, I rather prefer to ask than to pretend that I know .
Thank you in advance for your time and expertise.