If you have a good sized piece of sheet metal and some old cinder blocks laying around, you can dig a fire pit and put a row of blocks around it. Leave an opening to stoke the fire. build a fire in the pit and lay the metal on top. I guess an older model (70's or so) car hood would work. Anyway, get the fire going good, and throw a bunch of dead limbs, twigs and wood on top of the metal. As it heats the woods will turn black. You can break it apart and check, but when it is burned all the way thru, it is home made charcoal and will work in a forge, but you will need a bunch of it. The purpose of the metal is to allow the wood to char, but no burn up to ashes. If you don't have a squirrel cage fan for the forge, there are several plans on the net for homemade bellows.