How do I use Hedera?

You need only to install the extension for it to do its work.

As it says in the README, in order to see debug output, start Thunderbird, click on the icon in the status bar and select Preferences. Then check the Debug box and open the Error Console.

Hedera will output quite a substantial amount of information about what it's doing if it's working, or log errors if it's not. You can view the contacts that Hedera has pushed to Couch by opening $HOME/.local/share/desktop-couch/couchdb.html in a web browser and selecting the Contacts database. Contacts from Couch should also appear in the Thunderbird addressbook.

If you have enabled contact synchronisation between your machine and Ubuntu One (System -> Preferences -> Ubuntu One -> Services tab) then the contacts from your Thunderbird addressbook should end up in the Contacts tab at

  https://one.ubuntu.com/contacts