How to control temperature of a charcoal bbq
The temperature of a charcoal cooker is controlled by how much oxygen you allow to get to the fuel. I don't know what kind of grill you have, but typically there are one or more vents at the bottom, and one or more at the top. The bottom vents regulate oxygen supply to the fuel, while the top vents regulate air flow.

If you close down all the vents, the coals will eventually extinguish. If they are still holding enough heat, opening them back up will cause them to reignite. To regulate your temperature, open/close your supply vents (bottom ones) to varying degrees.

Also, consider setting up a zone on your grill surface where there is no charcoal underneath, to where you can move any food in danger of being overcooked.