I guess the biggest difference for users is that nostr relays don't federate with one another. So you'll have to query multiple relays yourself if you want to see stuff outside of the relay(s) you post to. The other big difference is that your identity is a keypair. The relays you send to only know your public key and that's it.

E: someone running a relay could still decide you need to create an account or something, but this account is only the permission to use this specific relay. Your identity would still be your keypair, so moving to another relay is easy.

Used nostr without much idea about itself, but using Amethyst, it was the easiest i ever created account ever in my life

The working involves relays ( which reminded me of tor ) which helps messages pass from you to others and from them to you.

Discovering accounts can be through their public key or as usual, their username ( if set ). Its usable with just the key generated during our signup.

The downside is not much active communities and users other than mainly crypto enthusiasts, but people are increasing.