First of all there is some confusion because blockchain doesn't play a role here.

You start by creating a pair of public/private keys. That is your "account" but is independent from everything else (e.g. not tied to any specific tool nor web service).

Then you create texts (notes) which are digitally signed with your private key. Using the public key anyone can verify it was you writing it and nobody else.

There is no blockchain in the process, these simple text messages get sent to a multiple number of relays (you can even host them yourself) and other people can read them very freely.

The main difference to mastodon is that exists no central server where someone registers an account and has the power to kick you out from the site (deplatform). This also solves the problem with the mastodon servers decides to stop the service and suddenly everything is gone.

On NOSTR your texts are your texts, and there are multiple copies everywhere (more than 1000 free relays at the momment).

Ahhh, that's a helpful explanation, thanks!

So with Nostr - it's decentralised to the point that I'm (me the user) the individual point that's sending et, rather than Mastodon which is decentralised less such that there's multiple servers with many users.