Books are great, but they're basically just a one way form of communication. If you have any questions that the book does not answer, Google is the best first place to go. Mailing lists and IRC are other great resources. Sometimes it's hard to formulate the right question, but there is help!
The extension website for this book can be found at http://vasir.net/openlayers_book. Current, up to date corrections and code fixes, along with more advanced tutorials and explanations, can be found there—and also on my blog at http://vasir.net/blog. You can also grab the code and more information about this book at Packt Publishing's website for the book, located at https://www.packtpub.com/openlayers-2-1-javascript-web-mapping-library-beginners-guide/book.
The OpenLayers mailing list is an invaluable resource that lets you not only post questions, but also browse questions others have asked (and answered). There are two main OpenLayers news groups—Users and Dev. The Users lis t is where the majority of questions are asked. Dev is reserved for development of the OpenLayers library itself. If you have questions about how to use OpenLayers, they belong in the Users list, not the Dev list . You can subscribe to the mailing list at http://lists.osgeo.org/mailman/listinfo/openlayers-users.
There are various ways to browse the content, and I prefer to use Nabble. You can view the lists at http://osgeo-org.1803224.n2.nabble.com/OpenLayers-f1822462.html.
Tip
Please do a thorough search before posting questions, as it is likely that a question similar to yours has already been asked and solved. If you have a question about using OpenLayers, please use the User list. Please do not post questions to the Dev list, unless it has to do strictly with development of the OpenLayers library itself.
When posting a question, please be as thorough as possible, stating your problem, what you have done, and the relevant source code (e.g. "I have a problem with using a WMS layer. I have tried this and that, and here is what my source code looks like..."). A good guideline for asking questions in a way that will best elicit a response can be found at http://www.catb.org/~esr/faqs/smart-questions.html.
Internet Relay Chat (IRC) is another great place to go if you have questions about OpenLayers. IRC is used for group communication; a big chat room, essentially. If you have exhausted Google and the mailing list, IRC provides you with real time with other people interested in OpenLayers.
Generally, the people who hang out in the OpenLayers chat room are very friendly, but please try to find an answer before asking in IRC. The server is irc.freenode.net and the chat room is #openlayers. You can download an IRC client online; a good Windows one is mIRC (http://mirc.com). More information about how to use IRC can be found at http://www.mirc.com/install.html.