Each Nostr account is based on a public/private key pair. A simple way to think about this is that your public key is your username and your private key is your password, with one major caveat. Unlike a password, your private key cannot be reset if lost.
The public key is generally presented as a string with the prefix
npub1 and the private key with the prefix
nsec1. Make sure you store you private key somewhere safe, like a password manager.
This tool converts Nostr public/secret keys to hex format, in your browser, nothing gets uploaded anywhere. Paste your key in the first text field and press “Convert”.