Hall voltage is generated in a Hall plate in the magnetic field when an electric current flows through the plate.
Average velocity with which the charge carriers move along the Hall sample to the other pole.
The magnetic field determines how strongly the charges are deflected due to the Hall effect and thus how large the Hall voltage is.
Distance of the edge of the Hall sample in which a negative excess charge is formed to the edge in which a positive excess charge is formed. In other words, it is effectively the height of the Hall sample.