All gas appliances are required to have a special valve located on the pipe near the appliance. Look at your gas cooking range – you should see a valve just behind the unit where the flexible connector connects to the pipe. Also, there should be a valve on the side of a gas furnace or gas water heater.
The illustration shows a typical gas valve that is operated with a small wrench. The valve may have a larger handle you can operate with your hand, and in some newer installations there may be a valve with a large handle. In essence they all work the same: when the handle is parallel to the pipe, the gas is on; when perpendicular to the pipe, the gas is off.
Make sure the valves are off and the pipe is capped if your home has a gas supply line with no appliance connected to it. If you ever smell gas in your home, leave immediately. Call for help from outside your home – you can call the local gas utility or the fire department.