The WCAG guidelines are intended to aid designers and developers with creating #accessible websites and apps. But it gets really technical really fast. So for beginners, I try to focus on the actionable parts of the guidelines, namely the P.O.U.R. concepts
(cc @JustineLom)
The first category in P.O.U.R. is Perceivable. This means that users must be able to perceive the information being presented – it cannot be invisible to all of their senses.