Make sure that the engine is cold. This is very important to prevent a fire.
Find the gas line and cut with tubing cutter.
Flare each end where you cut the tubing with the the flaring tool.
Install the valve onto the T and tighten.
Install the T in the gas line and tighten. Make sure the valve handle is easy to get to.
Flare a short piece of tubing and install onto the valve.
Slip the worm clamp over the length of rubber hose ( fuel line hose)and slide the hose onto the copper tubing.
Now make sure the valve is closed. Start your engine, place other end of hose in gas can and slowly open the valve.
When can is full, close the valve, remove the hose from the can and the valve. You can now continue mowing the lawn or give that neighbor a ride back to his truck.