How can I make charcoal?
Charcoal is organic matter (usually wood) that has been partially burned in a low-oxygen environment. To make it, you take wood, exclude air, and apply heat.
How to make charcoal with a fire and a metal container packed full of wood pieces
Supply list:

small pieces of wood (eg willow or charcoal)
a metal container with a lid and vent hole(s)
an outdoor fire pit or grill
fire tongs
firewood and kindling
an ignition method (matches, a lighter, flint &amp; steel &amp; tinder, a car battery, fire drill &amp; block, etc.)
the skill to start a fire using your chosen ignition method
a fire extinguisher or several gallons of water (in case the fire gets out of control)

Instructions:

Get a closeable metal container with no flammable parts (eg, an Altoid mints tin or a paint can). The container should close securely, but it needs a vent hole to allow gases to escape during the charring process. Poke an air hole in the lid if it doesn't have one.
Fill the container with pieces of wood. Pack them tightly together to minimize air space.
Get a good fire going. Put the container on the fire and surround it with hot coals or add logs around it so it will be surrounded by burning wood.
Maintain the fire while you wait. The wood will release wood gas as it chars, and the wood gas will catch fire as it comes out of the vent hole. You'll see a flame coming out of the vent hole(s) as if it was a gas stove. When that flame goes out, it means the charcoal is no longer releasing wood gas, which means it's done.

A very small container may take half an hour or less.
A large container such as a 55 gallon steel drum may take 6 or more hours.


Use tongs to pull the container out of the fire and put it on a heatproof surface, well away from anything flammable. Let it sit until completely cool before opening the container. Don't open the container while it's still hot or your charcoal will catch fire. If this happens, carefully try to put the lid back on to smother the fire. If you can't, now you have another small fire inside a metal container. Just let it burn, but stand by with your fire extinguisher or buckets of water to make sure this fire doesn't spread.


An even simpler method to make charcoal is just to have a wood fire. After the fire burns down, there will be some sticks or chunks of wood that didn't burn completely. The partially burned ends of those sticks will have a layer of charcoal. The charcoal may be covered with a layer of white or gray ash, which can easily be brushed or scraped off. Make sure the coals are completely cool all the way through before removing them from the fire, or you may have an unexpected fire in your art supply bag.
Common types of wood used for drawing charcoal are grapevine and willow. You can find more information about which materials make the good drawing charcoal here: Is coconut shell good to produce charcoal for drawing?
If you want a more detailed tutorial, there are lots of youtube tutorials about how to make charcoal. Here are just a few using different types of containers: paint cans; primitive method using a dirt mount; homemade kiln made from a 55 gallon steel drum.