The air is squeezed to many times normal atmospheric pressure. Then fuel, which is added through fuel injectors, is mixed with the pressurized air. The mixture of air and fuel ignites and burns continuously. Hot gas created by the combustion rapidly expands and pushes rearward, toward the exhaust. This gas is pushed past a turbine, which drives the compressor fans.
More air is taken in, and the remaining gas is forced out of the exhaust.
As the hot gases rush through from the rear of the engine, they create thrust. The level of thrust is one factor that determines the speed of the aircraft. The engine's hot exhaust, which can reach temperatures at or above 1,500 degrees Fahrenheit, coupled with unburned fuel from the afterburner, can burn a hole through the liner. Screech occurs when the hot air and fuel mixes with the cold air in the afterburner causing an audible vibration of about 200-500 hertz. If you had efficient mixing and combustion , there would be no screech.