Nostr itself isn't an app or website, but a protocol.
Think of it as a set of rules that allows different apps to communicate with each other in a decentralized way. It's designed for social networking and focuses on privacy and censorship resistance.
Nostter.app is a website that uses the Nostr protocol. From this website you can create a Nostr identity, post messages, and follow others. Since Nostr is decentralized, there are many other Nostr-based apps available.
Like Primal.net another website using the same protocol (using the same secret key),
What is a protocol? Imagine email. Email itself is a protocol, just like Nostr.
Different email providers like Gmail or Yahoo Mail are like the Nostter.app - they use the email protocol to offer their email services.
