To start a gas lawn mower, first move it to an open area and ensure that it has gas and oil. Ensure that the spark plug is firmly in place. Push the carburetor (a red/black button on the side) which pushes the gas into the lines. Pull the throttle to mid-length which helps keep it running until it warms up. Pull the starter upward in a quick and firm manner. For an electric lawn mower, of course the first thing to do is to make sure it is fully charged. The actual starting will depend upon the model, but most have a simple automatic start button. Easy, peasy!