To elaborate on that a little more, flash paper is treated chemically so that it contains traces of magnesium. The manufacturing process is extraordinarily dangerous if you don't have a professional lab and equipment, so put that thought out of your head right now.
When exposed to heat, flash paper doesn't just burn. It vaporizes. The burst of flames last only a few seconds and afterward there's nothing left. That should tell you how hot this stuff burns! The combustion is almost instantaneous so careful timing is a must. Magicians who haven't been careful find themselves with seared skin and I've heard some stories of second-degree burns as well. And let me tell you, there is nothing on earth that hurts quite like a burn wound.
Flash paper can be used in the open for switches with tissue paper billets and pellets (Jay Sankey's Spontaneous Combustion DVD is largely devoted to this concept), or it can be used covertly to create dramatic flashes of flame either for the sake of spectacle or to conceal productions and vanishes of objects.
If using the paper openly, a lighter is often good enough. But when working with the stuff covertly, you'll need a concealed ignition device. I've found one that uses a thin wire heated by en electric current from a 9 volt battery that I rather like, but most tend to use a flint wheel (as you see in Zippos and other cigarette lighters).