You take the URL for the Flash content (say, a video), copy it, open the app that can play some Flash, paste the URL in the app's browser and then have it go to the URL. If it can play the video, it'll load it and play it. You also can directly access a Flash website by typing the address in the app's address bar.
At least, that's how it works for me (I use iSwifter).
Marilyn