I'm always having to fix my grandpa's computer, but he lives 70 miles away.
So I set up Windows XP with remote desktop for him, and on the desktop, I put a shortcut to open an Internet Explorer window that goes to https://www.whatismyip.com/
When he calls me for help, he looks up the IP address first and tells me what it is so that I can remote desktop into his computer.
if you want to get tricky, you can set yourself up with a hostname through a dynamic dns service and get him VNC
you can listen on your side, program his side to connect to your pseudo-domain name, and with a simple click he can connect to you and you can take control of his stuff