Relays have 2 tasks:
1. Storing notes
2. Allowing people to query them

When you connect to a relay, it uses the WebSocket protocol to communicate (that is what the wss:// is). HTTP is like asking someone something and getting an answer, WebSockets are like real time chat.
Which is better for real time applications.

When you first make and sign a note, you send it to a set of relays. Each relay takes your note and stores it, and adds it to indexes, like:
- all kind 1 notes
- all notes by semisol
etc.

Now, you can ask for it! You ask the relay for, for example all kind 1 notes from who you follow, and it checks the indexes for those, and sends you the matching notes it found.

This is how a relay works. But on top there can be many features, for example:
- nostr.land charges a fee for writing
- many people host relays with whitelists
- aggr.nostr.land reads all notes from other relays, spam filters them and stores them
- hist.nostr.land retains multiple versions of events like a follow list
- relays like blastr or nostr.land broadcast your events to hundreds of relays