This page in the codex has a particularly interesting infographic that shows a flowchart of how WordPress chooses which template file it is going to use to render the page. For example, did you know if you have a published page with "contact" as the slug, it will look for and use page-contact.php automatically?
Unfortunately this graphic wasn't very pretty and for some reason has a giant "Page 1" text awkward sitting over it. We have an outdated version of this in the book, and since we are updating it right now, I thought I would take the opportunity to re-create this chart.
This will also be used in the book, which should be back available for order in around a week or so! Stay tuned!