Unfortunately, the book I usually point people to [1] when they ask a question like that is not yet updated for Drupal 8. Frankly, we're probably going to be in

Unfortunately, the book I usually point people to [1] when they ask a question like that is not yet updated for Drupal 8. Frankly, we're probably going to be in that awkward state where supply for learning resources for D8 is greatly overwhelmed by demand for a little while at least. But it's OSS; if all else fails, you can trace the source code, assuming you've got the PHP chops. 1: http://www.drupalbook.com http://www.drupalbook.com