What does user authentication mean with monzo I cannot activate my card
There is no such thing as activating a card with Monzo. If you have opened an account and received a card then you should be able to start using it immediately.
You do need to activate any new card after receiving it. Either by tapping your card on the back of your phone (on Android) or by inputting the card number.
You do. Instructions come with the card.
Edit: Sorry. Been drinking. Ignore me. As usual.