The Monterey Fruit Tree Spray Plus RTS comes with the sprayer conveniently attached and ready to use. The red knob you are referring to is turned different directions when starting and finishing the application. Please refer the instructions below.  1. Before you start, the blue top water flow valve should be in the "OFF" position, and the red product flow valve should be in the up, "OFF" position.   2. Shake container well and attach it to your garden hose. 3. Turn on the water from the faucet. 4. To apply, remove side pin (labeled "PULL OUT") and rotate red product flow valve to "ON"; then while holding sprayer at waist level and pointing in a direction away from face and body, push blue water flow valve forward to activate water.  5. When you are finished spraying or if you have to stop spraying at any time, press blue water flow valve with thumb to the rear to shut off water and return side red valve to the upright "OFF" position and replace side pin. 6. Turn off the water at the faucet. 7. Remove the container from the garden hose; then rinse thoroughly and store according to storage instructions.  View the full product label HERE for more information.