How does an automatic car gear work?

ArabiaWeather.com - The automatic transmission or automatic gearbox is known in our Arabic dialects as the "automatic gear", which is the part that automatically shifts the vehicle's speed, without the driver's intervention.

Invented by Felix Michael during World War II to help win the war, the first car with this technology was a limousine designed by Michael Felix for General Douglas MacArthur as a gift.

This type of transmission became common in cars in the 1990s, as it gives it a feeling of easy driving.. How does an automatic car gear work?