Entering a value for a homogeneous magnetic field allows to simulate the movement of a charged particle under the action of the so-called Lorentz force.
By activating the button "South Pole" or "South and North Pole" inhomogenous magnet fields are simulated with either one pole in the middle of the "floor" or two poles in the middle of floor and ceiling of the cube.
The latter settings allow to simulate the trapping of charged particles in inhomogeneous magnetic fields.