UX is a constant battle for Bitcoin in general. This is a very new feature built on top of cashu that is also very new.

The display simply describes what your lightning address would look like with npub by default or username if you pay to claim it

Npub@npub.cash or username@npub.cash

The claim username button and try it button will present options to log in with your nostr key.

Nip07 is browser extension signer option like alby

Nip47 is remote signer option like nsec.app

Nsec/ncrypt is where you just paste your nsec private key into the app