• The ‘device’ is the avast installation you are using at the time.
  • The ‘Your Account’ it is talking about is the my.avast.com web portal that you created, did you create one ?
  • The password it is asking for is the one you created for the my.avast.com account/portal.

In the avastUI > Settings > General - Avast Account Status. It will tell you if that installation is connected to an account or not. See attached image, mine is connected to my.avast.com account, yours will probably show not connected/connect (or words to that effect).