Check out our Frequently Asked Questions. If that doesn't cover it, the best way to get an answer is to post your question in the appropriate Forum. (We are notoriously bad at answering email, but we do have a moderator checking the forums a couple of times a day, except on weekends and holidays.)
Most technical difficulties with our books are handled with this article: Problems with viewing and printing our books, but if that doesn't resolve it, please post the difficulty in the appropriate Forum.
Suggestions and errors:
If you have suggestions, or if you find any errors, we would be very grateful if you could post these in the Forums.