I am a flintknapper, and have been doing it for 13 years now. It is a valid survival skill, but it's application has some limits.
If you are not in an area with a supply of flint, there are several options. Human refuse can provide glass. Bottle bottoms are a good source of arrowhead sized pieces, and are fairly easy to work. Many areas will have quartz pebbles and cobbles that can provice a sharp edge. Fine grained basalt works well, and is often found in big pieces.
Even 3/4" pebbles can make a good tool by using the bipolar technique......
This means taking two larger stones, preferably of tougher, less glassy material, and using them as a hammer and anvil to break the pebbles nutcracker style. If you do this right, an acorn sized pebble of quartz or chert can yield 5 or 6 little razor blades. One blade will pop off at each impact, you are trying NOT to shatter the stone.
Do not plan on producing a "Stone Knife" Think instead of producing a tool box full of easily altered flake blades from a stome core. This is the technology that worked out very well for the Neanderthal people for tens of thousands of years. In one afternoon, you can learn to produce tools equal to theirs!