Maybe look at Michael Wittmans YouTube- Bluesky-biochar

Also weedy garden had a good basic video on it.. https://m.youtube.com/watch?v=vAJt5tGwNVM

Also there was a guy in the finger lakes region of NY with some awesome biochar videos but I can't remember his name. He was mostly doing small batches in his wood stove

Basically it’s the left over cold coals and ash from burning wood (fire).

The coals are very porous and therefore hold water, air (O2), and provide homes for beneficial soil microbes.

The ash is the raw minerals that the fire was not hot enough to convert to gas form.

That becomes nutrients your plants absorb and in turn feed you nutrient dense food

It’s wood that has been charred, at a constant temperature for a period of time just below its combustion temperature. When it comes out it has a special characteristic that makes it great as an amendment to soil. Biochar has a whole bunch of tiny spaces inside it to hold: moisture, nutrients, enzymes, lots of cool stuff that replicates over time.

So when you place it in your soil it can benefit your crops for many years to come. Not all biochar is the same if it’s not prepared the right way tho. Not an expert, just took a class once. The place I went was in NC. Very neat ancient technology . Not sure if helpful but try this https://biochar-us.org/welcome-biochar-learning-center

Forgot one other https://wilsonbiochar.com/