J=σE
Where j is the current density, e is the electric field in the conductor, and σ is the conductivity.
When an electric field is applied inside a conductor, the free electrons in the conductor are forced to accelerate. However, the free electron itself has thermal motion, and the research shows that the thermal motion of the electron is very fast and irregular, so it has collided with other particles in the conductor many times before being completely accelerated and decelerated by the electric field. However, it always tends to move in the opposite direction of the electric field. From a macro point of view, all free electrons move in a certain direction at a constant speed (slowly), forming a stable current.