Firesteel is a piece of high-carbon steel used for striking a spark, usually kept in a tinderbox together with flint and tinder. From the Iron Age onwards, the use of flint and steel was the most common method of fire lighting prior to the invention of the friction match.
More recently the term 'firesteel' has become synonymous with so called 'artificial flints' which are metal rods of varying size composed of ferrocerium, an alloy of iron and mischmetal. Mischmetal is an alloy primarily of cerium that will generate sparks when struck. Iron is added to improve the strength of the rods. Small shavings are torn off the rod with either a supplied metal scraper, a piece of hacksaw blade or commonly the back of a knife ground at a suitable angle. These shavings then ignite at high temperatures, and are much more effective than their historical equivalent.
While it takes practice and properly prepared tinder to create a sustained fire, the modern firesteel is considered by survival instructors and serious outdoorspeople to be one of the most reliable ways of making fire in severe conditions. Two good examples of firesteel are made by Light My Fire and Blastmatch. The sparks produced by these products are extremely hot, 3000 C°(5500 F°), and easily light toilet paper or small pieces of wood or commmercial tinder products.
Traditionally a flint and steel were used. However, the flint was not the important part. With a proper striker, you can get sparks off of any hard, non-porous rock that has a sharp edge, even pertrified wood. The spark comes from shaving small pieces of steel off of the striker, with enough friction to heat them up to red hot. Charpaper can be used as an intermediate step between the striking and the tender. Charpaper will catch a spark, and glow, but it will not ignite. In order to get fire, you would hold the glowing charpaper against your tinder and blow on it. This works much better than attempting to get a spark to stay on the tinder.
In order to use a flint and steel, you take a hard rock, with a sharp edge in one hand, and the steel striker in the other. Hold the striker loosely, and strike it against the rock in such a way as if you were trying to shave the striker with the rock. if using charpaper, place the charpaper on top of the rock, and it will catch the sparks. You then take the glowing charpaper, and set it against your tinder, and blow on it gently until you get a flame.