Remove any stimuli of pain. The first part of the theory is that if there is no pain stimuli, there is no pain. The idea is that the stimuli opens the gate that sends signals from the spinal cord to the brain. A stimulus can be anything that causes harm to the body. Without a stimulus, there will be no pain -- the gate will remain closed.
Activate large nerve fibers. These are activated through non-painful stimuli. An example would be a soft touch. The idea is the large nerve fibers activate projection neurons which would open the gate -- but they also activate inhibitory interneurons which counter this reaction and cause the gate to remain closed. Since the gate remains closed, no pain signals will travel to the brain.
Activate small nerve fibers. Through the use of pain stimuli, small nerves become active. This activity causes the projection neurons to be active and blocks inhibitory interneurons. Therefore, the inhibitory interneurons are unable to keep the gate close and the signal travels to the brain.