The Americans with Disabilities Act (ADA) Standards for Accessible Design applies to certain websites, but it's good business sense for every website to comply. You wouldn't want to exclude anyone from visiting your website and converting.
The World Wide Web Consortium (W3C) created international standards for website accessibility. The W3C website has a validator to check compliance of your HTML and XHTML.
Images and Video
ADA compliance is good for SEO. If you have a video on your website, neither a deaf person nor Google can hear what is being said. Adding a transcript will allow someone to understand what the video is about. A transcript is also full of relevant keywords for Google. Additionally, every image needs ALT text and a caption unless it is a decorative graphic so assistive technology, such as a screen reader, can explain the image to a blind person.
Content
Use heading tags and present your content in a logical order. Do not use images for text unless it is part of your logo. This is also important for SEO.
Font should be at least 16 points and a person should have the ability to resize it up to 200 percent without affecting their ability to use the site.
Color
Do not rely on color alone to convey meaning; use common shapes as well. Design for people with color blindness. When creating charts and graphs, use textured patterns in addition to colors to show contrasting data. There are also certain color combinations to avoid which won't affect your aesthetics. Run your site through a color blindness simulator to check for potential issues.
If you have a WordPress website, there are multiple plugins which can help you determine if your website is ADA compliant and make the necessary changes. Do not depend on plugins if you must legally have an accessible website, hire a web design firm specializing in DA compliance. For more information click here https://www.inc.com/carol-sankar/7-ways-to-make-sure-your-website-is-ada-compliant.html.