Hello,
I suppose for example you have subscribed for the French defence (two good choices...1. you have subscribed 2. you chose a very good opening

)
- You click on French at the left of main mage
www.chesspublishing.com - Now you view last update webpage (currently J.Watson's "French Defence Update May 2012")
- Then read what is on the right side of the page (written in red color) : "PDF eBooks", "Playable ebooks", "PGN Games archives"
- Click to "PDF eBooks" to find what you're searching for....click on "Advance KIA" to view or download PDF file about this sub-variation of the French, click on "Tarrasch" for that other and so on
'eBooks' is a merchandising word meaning "electronic books", merely files on computers you can print to get paper books
"Playables ebooks" are in fact chess archives files....you can open or read them with Chessbase software...."playable" means more: you can browse these chess games databases. "cbv" is one file extension for such files.
"PGN Games archives" are for ASCII (=text) files databases "pgn" is one file extension for such files.
Now I foresee next question:"can I download all PDF files (those I can access with my membership rights)"...my answer: I don't know.