Coal is mined either through underground or surface mining. Underground mining requires digging a shaft to where the coal seam is found. The traditional room and pillar method requires leaving pillars of coal in place to help support the mine roof where miners work. Unfortunately, this method leaves more than half the coal in place. Improved mechanization and longwall mining, which uses hydraulic roof supports, have since increased the amount of coal able to be extracted.
Here is a link that might be useful: Coal Mining