Virtual cards do not need to be activated and can be used immediatly after you created them online. However, physical cards have to be activated before you can use them.
Once you've received your physical card, go to the 'Cards' section on the left of your Qonto home page. Select your new card and then click on 'Activate this card' in the tab on the right.
You're asked to type in the ID number of your card in order to finalise its activation. This ID is located on the back of the card, just above the signature zone.
You can now process payments and withdraw cash with your card!