A quick search yielded this video, which seems straightforward enough.
I have never seen anyone use charcloth like in the video, but it seems to work nicely.
To summarize the video:
- Place the charcloth on top of the flintstone with your fingers.
- Strike the flint until the charcloth is lit.
- Put the glowing charcloth into a tinder bundle (old rope that has been pulled apart, wood shavings, dryer lint, cotton wool, etc.) and blow gently until you have a flame.
- Slowly add more fuel to the fire. Start with small twigs, dry grass, etc. until the flames are high and hot enough to add firewood.
Most importantly, have something that immediately starts glowing or burning, like wood shavings etc. Start the fire by igniting the smallest fuel at hand and build your way up from there.
You might consider "cheating" using wax paper or a magnesium bar, which can be bought online or in outdoor equipment stores.