Welcome to the party! You are in the right place.

You are interacting with #Nostr through a particular client that happens to look a lot like Twitter. There are other clients that look more like Reddit, or that look like a podcast player, or music streaming service... They're all Nostr clients, though, and you can log into all of them with your private key, though we would recommend using an app like #Amber on Android, or a browser extension for web apps. You should avoid putting your private key itself into every app you come across.

Some clients include a marketplace, others include live-streaming, and others are for audio chatting. There are a MASSIVE number of different types of apps and experiences, and you'll want to explore.