When I was first learning about accessibility on the Web, I stumbled across WebAIM (Web Accessibility In Mind), a fantastic resource for all things accessibility.
They have a ton of great articles focusing on different aspects of web accessibility, but one of my favorites I keep going back to is Constructing a POUR Website. It helps unravel the Web Accessibility Guidelines principles of accessibility and helps shift the focus away from how to make content accessible to why.
In summary, the WCAG guiding principles state that accessible content is perceivable (people can perceive the content with any of their available senses), operable (people can interact with the content as needed), understandable (people can understand the content and how to navigate it), and robust (the content can be interpreted by an array of technologies). These principles form the acronym POUR, which is an easy way to remember them.
To explore these principles in more depth, check out the article. And if you have any questions or would like to discuss it, feel free to reach out to me on Twitter.