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.