The transmission is a group of parts that transmits power from a vehicle’s engine to the drive axle, which in turn makes the wheels go around. If you do not use a clutch to switch gears, your vehicle has an automatic transmission. If you use a clutch, your transmission is manual.
Automatic transmissions contain an oil-like fluid to cool and lubricate the mechanism. The level and quality of this fluid should be checked regularly (see your vehicle owner’s manual) and replaced if needed.
If your transmission performance seems good, the fluid is clear and red, and you have not had to add fluid, leave your transmission alone.