You go to the Editing menu on the top bar and click Add Work, then you enter the information and after the work is created you can link it to the recording on the CD: from the work page, by clicking Relate To and searching for the recording (remember that you can copy the recording url -or any url- and paste it on the "Relate to" field, if you don't want to search or you can't find it). You can do it the other way around, from the recording page link the work, it doesn't mather.
For what I can see you already added the work, all you need to do is link it to the recording as I just described and then link the work to the authors in a similar way (here too, you can do it from the work page and search for the artist or do it the other way around, and you can copy any url to the Relate To field)
Was that clear?
If you want to add works for all the tracks on teh album (so to add writing credits) there are scripts to make it eaisier.