So in places where trains are done well, like Asia, every real estate listing will describe how far it is to the nearest station, because it's taken as a given that that's how you want to get around. If you're mobility impaired you'd probably prioritize one of those locations so you don't have to go as far, but you're on luck because that's also where the most supply is available as the train operators are also developers. It's also where most of the destinations are so you might not even actually need to board a train most of the time.

But I guess to directly answer your question: ideally you get to the train by taking your electric wheelchair along a nice shady pedestrian area, amply separated from any cars so that it's quiet, and conveniently crossing at most two lanes of traffic at a time. But it depends on what your area is like.