He's just saying to put the diodes pointing into the high and out of the low voltage from the lines connected to the inductive load. Under normal circumstances the lines to the actuator are at a higher voltage than the low end so no current will flow through the diodes, likewise the voltage at the actuator is normally lower than the voltage of the high end of the supply, so no current will flow from the actuator lines to the high end. The diodes allow current to flow into the high voltage or out of the low voltage supply, this means if a spike jumps above your intended supply it simply shorts to high and if it spikes below the low supply, it simply shorts to low. It's like a water tank with a float valve near the top that drains water and one near the bottom that adds water, the water level ends up staying between the two.
Sorry if I over explained I'm just trying to make it clear.