Adding a carddav addressbook to Roundcube

Login to your Roundcube and go to Settings -> CardDAV. There you have the following fields:

Name of the addressbook Enter any name you want to identify your addressbook
Activate CardDAV- Addressbook Tick the box
Username Enter the username provided by Netuxo or your domain administrator
Password Enter your password provided by Netuxo or your domain administrator
URL https://baikal.netuxo.coop/html/dav.php/addressbooks/<username>/default/
Replace <username> with the one provided (see above)
Update interval (hours) Leave as is, or edit as to your liking
Remove this addressbook Only tick it you want to remove the addressbook from Roundcube.
Note: this will not remove the addressbook. It will only no longer be available in Roundcube.

You can add as many carddav addressbooks to your Roundcube, including ones provided by other carddav providers.