Flint knapping is the art of chipping off flakes of flint to make arrowheads, spear points, fur scrapers, and so on.
The art dates from primitive times. Flint, along with bone and antler, was one of the few naturally occuring durable materials. Flint is very hard and brittle, and tends to break into flat pieces with very sharp edges.
To knap flint, you need a flint nodule and a hammerstone. A typical flint nodule is round, covered in whitish-grey stone, and is often found near limestone and shale. Hold the nodule between your legs, resting it on the ground. Strike the flint with the hammerstone, using a glancing motion. At first, your strokes should be rough, to remove the outer coating. When you strike actual flint, (a dark grey, flaky textured material), you should strike more carefully.
Whereever you strike, the flint will break off horizontally, shearing away from the nodule. Try to get triangular pieces to flake off. A bump will form, known as the percussion mark, where you hit the flint.
For more detailed work, use an antler (or similar object). Wedge your antler on the flint, and then hit the other end of the antler with your hammerstone, directing all of your force to a single, precise location.
A skilled knapper might be able to get 20-40 seperate usable pieces, known as points, from a single nodule.
There are actually festivals, known as knap-ins, where knappers from around the world meet to beat rocks together.