The pump will come with a nozzle that attaches to the valve. For Schrader valves, simply press the nozzle onto the valve stem and flip the lever to lock it in place. For Presta valves, unscrew the valve cap and press the nozzle onto the valve stem. Then, flip the lever to lock it in place. Make sure the nozzle is attached securely to prevent air from escaping while pumping.