Flint and Steel are some very easy materials to get a hold of in many situations and often times you even have the steel with you in the form of a knife, hatchet, key, or even a steel aglet on your shoelace. The hard part is finding the flint and using it properly.
Where to find Flint
Flint is a hard sedimentary rock. It can hold a very shard edge and was often used as a knife. Flint is often found in areas where erosion has occurred. Be sure to check in river beds, eroded ditches and even freshly plowed fields. It is a dark grey to grey rock and is often found in chucks or pieces.
How Flint makes a Spark
When flint scrapes across steel, the sharp edge of the flint scrapes small pieces of steel off and through the heat of friction ignites the steel particles. The sharper and better applied the flint, the more sparks. Obviously, this same process does not work with aluminum and many other metals. And actually, any rock as hard as flint will make a spark (obsidian, quartz, diamonds, etc).
How to start a fire with Flint and Steel
To make a spark with flint and steel. Grab your piece of steel, and then strike your flint against it until you are able to produce sparks. You should try to gather your kindling in a small birds nest type shape to catch the sparks you are creating.
Once you get one spark that seems to have caught in the birds nest and is producing some smoke, then blow the spark gently until a flame results. Then placing the flaming birds nest into your pre-made fire structure and tend it into a fire.