Look man here is what we'll call the "Energy Transfer Path". Otherwise known as using the engine and transmission to move forward or backwards.
Engine>Torque Converter>Internal Gearing of Transmission>Final Drive Gears(at the second final drive gear power going to the pass. side is now turned towards the back of the car and towards the diff)>Transfer Shaft towards the diff>diff>axles>wheels.
Basically the final drive gears take the energy going from the actual gear process gives them a u-turn so that you can drive the car forward or backwards. IM me if you'd like me to explain it better. But it is pretty simple. Just dont let the word "gears" confuse you anymore.
