Start a fire at the base & then add stuff until it gets burning good & hot.

Wood turns first to charcoal (with heat) & then slowly to ash (with air).

You'll want to be slowly adding wood/feedstock as it breaks down into charcoal. Add it too quickly & you'll have a lot of black wood that hasn't properly pyrolised. Add it too slowly & you'll have more ash & less charcoal.

The timing of top ups varies based on what you're burning. It looked like you had a lot of hardwood stumps which burn slowly. Generally you wait until a layer of ash starts building on the top of the wood before adding more.

I always struggle to get the big hardwood chunks charred properly (you just recycle them into the next burn).