By far the best first step you can take is to try it yourself. Follow a ten-minute tutorial on how to use one (Rob Dodson has good introductions, such as this one on VoiceOver - this is really a case where videos work best to learn), and then see if you can manage to navigate your web app using it. Ideally even with your screen turned away, but that's probably too had at first, and also makes it hard to see what's going wrong.