The simplest way I’ve explained relays to myself is that relays are very similar to telephone companies like vodafone, verizon, t-mobile etc.

You need a telco to receive and send info to the nostr network.

A couple differences between nostr relays to telcos: you can and most use more than one telco, and it is possible that you and another nostrich on the nostr network have no telcos in common, making communication difficult, or not possible!