In some of the latest cars in the marketplace, you can change gears by simply pressing a button, turning a knob or toggling a little joystick. Yet simultaneously, plenty of different automobiles still require motorists to use one foot for the clutch pedal and another for the gas, all while using one hand to control the gear-change lever through a definite pattern of positions. And several other current vehicles don't possess any traditional gears at all in their transmissions.
But regardless of whether a vehicle has a fancy automatic, an old-school manual or a modern-day continually variable tranny (CVT), each unit has to do the same job: help transmit the engine's result to the driving wheels. It's a complex task that we'll try to make a bit simpler today, you start with the basics about why a transmission is needed in the first place.
Let's actually begin with the normal internal combustion engine. As the fuel-air blend ignites in the cylinders, the pistons start moving up and down, and that movement can be used to spin the 
car's crankshaft. When the driver presses on the gas pedal, there's more fuel to burn off in the cylinders and the whole process moves faster and faster.
What the transmission does is change the ratio between how fast the engine is spinning and how fast the driving wheels are moving. A lower gear means optimum Variable Speed Transmission performance with the tires moving slower than the engine, while with a higher gear, optimum performance comes with the wheels moving faster.
With a manual transmission, gear shifting is handled by the driver via a gear selector. Many of today's vehicles possess five or six forwards gears, but you'll discover older models with from three to six ahead gears offered.
A clutch is used to transmit torque from a car's engine to its manual transmitting. The various gears in a manual transmitting allow the car to visit at different speeds. Larger gears offer plenty of torque but lower speeds, while smaller sized gears deliver less torque and invite the car travel more quickly.