Coal cooking

I presume you are referring to charcoal and not petroleum based coal...

You cook, switching between direct and indirect heat sources, to allow the meat to cook until it is done.

Knowing when you reach that point is a skill that you learn and understand as you cook time and time again. Soon you can judge when a steak is rare or medium rare with the light touch of a finger. Others meats like chicken and game hens should be checked with a thermometer to insure food safety.

Some divide the grill in half using fire bricks or metal. This gives them half of the grill for direct heat and half of the grill for indirect heat. This allows them to cook the meat evenly as they switch between direct and indirect.

See:
https://www.weber.com/US/en/help/grilling-tips/direct-indirect/

https://www.weber.com/US/en/grill-skills/mastering-basics/charcoal/fire-configurations

http://www.thekitchn.com/whats-the-difference-between-direct-and-indirect-heat-232731

I will add as MadMan said, an instant read thermometer
has Upped my game 75 %, especially on delicate pork chops
I nailed a Fillet nearly perfectly this weekend, due to the therm...
and reverse sear....