when I addForce to a ridigbody, does the force stays for the whole game or I need to add it every frame?
If there’s Drag or Friction being applied on the Rigidbody, it will eventually lose the energy that it gained when you applied the force to it.
If you want to make something move as long as a button is held down (like moving a player forward by holding the W key down), you’d want to apply the force in the FixedUpdate() method.