Show this to yourself with the water analogy.
Turn the garden hose on with the spray nozzle shut. Pressure in the hose is what? Same as the pressure supplied by the city or well pump.
Taking this further, connect the hose to a sprinkler.
The pressure in the hose when its running will be slightly lower but pretty close to house pressure.
Restrict the hose or supply (aerator in the faucet or pinch the hose).
That pinch causes a pressure drop when the sprinkler is running.
Shut the sprinkler off and what happens to pressure thoughout the hose?