
...
What is Nostr?
Nostr is a protocol, designed for simplicity, that aims to create a censorship-resistant global social network. Let's unpack that a little:
Simple
The protocol is based on very simple & flexible event objects (which are passed around as plain JSON) and uses standard elliptic-curve cryptography for keys and signing. The only supported transport is websockets connections from clients to relays. This makes it easy to write clients and relays and promotes software diversity.
Resilient
Because Nostr doesn't rely on a small number of trusted servers for moving or storing data, it's very resilient. The protocol assumes that relays will disappear and allows users to connect and publish to an arbitrary number of relays that they can change over time.
Verifiable
Because Nostr accounts are based on public-key cryptography it's easy to verify messages were really sent by the user in question.
Like HTTP or TCP-IP, Nostr is a protocol; an open standard upon which anyone can build. Nostr is not an app or service that you sign up for.
...
Nostr, a simple protocol for decentralizing social media that has a chance of working
A guide to the simplest decentralized protocol that isn't peer-to-peer, therefore works.

That page includes a link to find client apps for a variety of platforms. I looked at the guide for Gossip - the desktop application and it did not seem very user friendly/intuitive yet (wrt relays).
It's still a developing project, so I expect it will get better/easier or fail.