If the light source comes from behind, or at the back of the reflector, then the reflector catches the light sent out from an LED at various angles to focus it into a forward beam. Most flashlights use this method.
If the light source comes from in front of the reflector (recoil), then it works like a satellite dish to capture the light and focus it. I believe this method generally has lower efficiency in terms of focused light in the beam.
Another approach is some lights depend heavily on a special lens that focuses the light into a tighter beam. In this case, the distance from light source to lens will be important.
You can get a little info on some of the terms above and more at: