Your gear linkage is offset!!
Or you are on a steep down hill
A vehicle moves forward when in drive due to the transmission transferring power from the engine to the wheels. Possible causes for a vehicle not moving forward in drive could include low transmission fluid, a faulty transmission solenoid, a defective torque converter, or a worn-out clutch (for manual transmissions).
The engine causes the tires of the vehicle to turn. The tires are made of rubber in order to maximize the friction (traction) between the tires and the concrete. It is the tires and the force of friction which causes a vehicle to move forward (or backward, for that matter).
It's in "reverse."
When a bird walks or hops it moves forward
If your car moves forward when the gear selector is in reverse, it could indicate a serious issue, such as a malfunctioning transmission or a problem with the gear linkage. The reverse gear might not be engaging properly, allowing the car to move forward instead. It's essential to have your vehicle inspected by a qualified mechanic to diagnose and fix the issue, as it can lead to dangerous driving conditions.
Having it on "PARKING"
no
inertia
Need more info. Are you saying that? 1. The vehicle won't go into reverse? 2. The vehicle shifter won't go into reverse? 3. The vehicle shifter won't move into reverse or drive?
when the vehicle suddenly start the person move backward and when the vehicle stop the person move forward
Check transmission Fluids.
have your transmission checked, you need a new one.