Our coverage of the sample code was not meant to be extremely thorough; just enough to give you an idea of how it works. We'll be covering OOP concepts in more detail throughout the remaining chapters, so if anything is a bit unclear, don't worry too much.
As OpenLayers is a library and provides functions for you, it is important to know what these functions are and what they do. There are many places to do this, but the best source is the API docs.
The API documentation is always up-to-date and contains an exhaustive description of all the classes in OpenLayers. It is usually the best and first place to go when you have a question. You can access the documentation at: http://openlayers.org/en/v3.0.0/apidoc/ for the 3.0.0 release. It contains a wealth of information. We will constantly refer to it throughout the book, so keep the link handy! Sometimes, however, the API docs may not seem clear enough, but there are plenty of other resources out there to help you. We'll cover a bit about how to find your way in API documentation in Chapter 2, Key Concepts in OpenLayers and in Appendix A, Object-oriented Programming – Introduction and Concepts.
The extension website for this book can be found at: http://openlayersbook.github.io/openlayersbook/. Current, up-to-date corrections and code fixes, along with more advanced tutorials and explanations, can be found there. You can also grab the code and more information about this book at Packt Publishing's website, located at https://www.packtpub.com/web-development/openlayers-3-beginner%E2%80%99s-guide.
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 were two main OpenLayers news groups—Users and Dev for the OpenLayers 2 Version. There is a list only for OpenLayers 3 development discussions located at https://groups.google.com/forum/#!forum/ol3-dev. You may find some users' questions in the archives as it was before for both development and users questions.
Now, user questions should be only posted on http://stackoverflow.com and tagged with openlayers. OpenLayers 3 library developers will answer directly here.
When posting a question, please be as thorough as possible, stating your problem, what you have done, and the relevant source code (for example, "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.
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, your favorite search engine is the best place to go to. The Questions and Answers website http://gis.stackexchange.com, the young brother of StackOverflow, dedicated to GIS (Geographical Information System) can also be quite useful. But, at the end, don't forget that mailing lists and IRC are other great resources.