Imagine a charge travelling circularily
about an axis builds up a magnetic
moment
It rotates (spins) about its own axis (the
blue arrow) and precesses about the axis
of the magnetic field B (the red arrow).
The frequency of the precession (w)  is
proportional to the strength of the
magnetic field:
w  = g B0
g = magnetogyro ratio
  Magnetic field mrasured in Tesla
 1 T = 10,000 gauss