Web Content Accessibility Guidelines are created by World Wide Consortium (W3C) with the purpose of providing a set of standards for making the Internet more accessible by improving the user experience for people with disabilities. The recent version WCAG 2.1 was released in June 2018.
Accessibility Guidelines WCAG 2.1 Cheat Sheet
How to use WCAG 2.1?
The best way to do it is to scrutinize each page of your website or application against the WCAG 2.1 success criteria. There is plenty of WCAG checklists and tools enabling to automate the testing process.