Someone talk me through making your website ada compliant?

Two that people forget: PDFs and video. A scanned PDF is just a picture to a screen reader, so anything important in one needs a proper text version. Video needs captions, and the auto-generated ones need checking - they get names and numbers wrong constantly. I'd also put up an accessibility page with a contact address for anyone who hits a problem. You hear about issues from a user instead of from a letter.

The thing nobody tells you up front is that the ADA itself does not contain a technical spec. What everyone builds to is WCAG at level AA, and if somebody is writing you a requirement, that is the standard to ask them to name. Practical order on a client site: keyboard only first - unplug the mouse and try to get through the nav, a form and any popup. Then alt text on images that carry meaning, real labels on form fields, colour contrast, and headings that run in order instead of being picked for their size. An automated scanner finds maybe a third of it, so a green score is not done. I would stay away from the overlay widgets, they have not gone well for the sites that bought them.