The United Kingdom's Information Commissioner's Office has just released a guide to understand the GDPR. A good official guide (in the sense that it is published by a regulator) for those who are struggling to understand the concepts introduced by the GDPR.
I knew something was on the way but I wasn't aware that it was here already (says the one who has just trawled the Article 29 Working Party guidance on breach notifications and might not have bothered if he'd been aware of this!)