Common propane tanks, also referred to as cylinders or bottles, that are used for gas grills are typically 20-lb tanks. The propane supply to the grill should be turned off after each use. Cylinders used to supply home cooking appliances with propane need not be turned off after each use, but need to be turned off if the appliance won't be used for extended periods or when the cylinder needs to be changed. Keep propane tanks in good working order so the gas valve performs as expected. Leaking propane containers are extremely dangerous.
Inspect the propane tank. Wipe dirt and foreign material from the top of the tank around the gas valve and from the gas valve itself with a rag.
Locate the "Off" indicator arrow on the tank at the gas valve.
Grasp the valve, and then turn it in the direction indicated by the arrow (likely clockwise) until it won't turn anymore.