have a look at this:
Audiobook Tag Issue
To call an action:
Select the files in the files list and then select the action from the actions menu.
I suspect that you first have to fill tags before you can apply actions to the files.
A way to fill a lot of files with the same data (but still fill them) is to select all the files in the files list, enter the data in the tag panel and press save (Ctrl-S).
You may then continue with the actions as described in the post I mentioned above.