A new presentation explaining the basics of how email authentication works is available from DMARC.org. The concepts and common usage of SPF, DKIM, and DMARC are all covered in this introductory slide deck, which is made available under the Creative Commons Attribution-ShareAlike 4.0 International License (CC BY-SA).
You can download the 1.9MB PDF file clicking on this link, or by navigating to our Articles, Tutorials and Videos page and checking under the Presentations section.