Hmmmmmmmm, you could think of it like that but I think it's more.

Your npub is the address box that relays will send notes to when your client (Damus?) calls out to them.

Your nsec is the key to your address box and it also signs your notes that you send to the relay as yours.

Public key private key cryptography's a biatch.

Spend some time with ChatGPT to grok.