"learned to make charcoal"

It is a sign of Ger's trust in Beauty's ability that he teaches her to make charcoal. A blacksmith's shop requires vast quantities of charcoal to run smoothly, so Beauty's ability to make charcoal serves to provide fuel for Ger's forge as well as for their home. Charcoal is produced by heating of materials such as wood or bone char in a contained, oxygen-free environment.

After removing fallen trees with Greatheart, Beauty would have had easy access to wood for charcoal production.