My charcoal is constantly at a zero, how can I fix this, I see charcoal increasing from the storage..

You will have 1 charcoal workshop that runs on its own and a number of charcoal factories. The charcoal factories need to be filled with lumber in order to run and produce charcoal. Tap on the buildings and select the Transport option. You can then send lumber to the building. Do this with all of your factories. They need to be refilled every time they run out. Or when your charcoal supplies are low.

Depending on what you need to do you don't always need to have the charcoal factories running but it can affect the production rate of your other resources if you don't.