The best explanations of relay I found was an youtube video comparing it to a hose where water flows.

So you want to spread water around (your notes) and you do it by connecting your water source to many hoses.

When one ges broken or blocked the others keep sending water.

I don't remember the name of the video, but it was fantastic and it's the analogy I use with people and they all want to try nose after that.

If you know graphs you can days each user is a a node and and relay is an edge, and you have unlimited amount of edges between any nodes