There are three contributions to the hyperfine field:
*) orbital contribution: imagine an electrically charged ball on a carousel and a child standing still in the middle of the carousel: the child will feel a magnetic field due to the orbiting charge.
*) spin-dipolar contribution: imagine a bar magnet at the side of a non-turning carousel. This will induce a magnetic field at the centre of the carousel where the child is positioned.
*) Fermi contact field: imagine that the child has some bar magnets in its pocket with the amount of spins up not equal to the spins down. This leads to a third magnetic field contribution