Put you’re sample in an external magnetic field with a specific direction and irradiate it with microwaves. Vary the strenght of the magnetic field to become the absorption spectrum with respect to the applied magnetic field. From the peak in this spectrum the g factor can be derived for that specific direction of magnetic field.
Now change the direction of the magnetic field and repeat the same procedure. Plot the measured g-factors w.r.t. the direction of the magnetic field to obtain the EPR experiment pictures.