Re: question about books
You can download "Op Amps for Everyone" by Ron Mancini for free.
**broken link removed**
It also contains a chapter about active filters design techniques (chapter 16), but this is probably not the best introduction to filters for a beginner. I suggesst you look at this book for a few hours. If there is anything about Op Amps you are missing there (or that you don't understand) post it here, and people may refer you to further books.