I started with a large batch of sticks for fuel. They had been cut live from mulberry, willow, tulip poplar and pear trees, and allowed to completely dry. They were a bonus of my tree pruning efforts.
To make charcoal, you must limit the oxygen supply to the fire. I did this by settling the bottom half of an old charcoal grill into a hole in the ground, then burying the edge of the lid once the fire was going. I left a small area unburied to let a little air in.
Once the fire was going well and the lid was on, I found that it didn't pour out much smoke, so I started a fire on top of the metal lid as well. That did the trick. Smoke poured out of the small hole. I kept it burning for about three hours. Then I let everything cool down.
When I opened up the grill, I had about 10 gallons of perfect charcoal.
I crushed the bigger pieces so that they would be uniform, a bit smaller than a charcoal briquet.
I mixed the cooled charcoal with aged humanure and other compost, some rabbit manure, and fresh urine. I added water to create a slurry in which any organisms could colonize the charcoal, and left it overnight.
I mixed scoops of the inoculated charcoal into the soil around some of the fruit trees in my orchard. I hope it helps! This was an unscientific experiment because I kept no exact records, and I did not have a control group for comparison.