First of all, you must have a Deezer account and then you must enter the credentials in the Bang & Olufsen app to log into the account on your music system. If you do not have a Deezer account, you can sign up via the Deezer webpage:
http://www.deezer.com
Note that Deezer may not be available on all markets.
*How to add your Deezer credentials to the Bang & Olufsen app
