Open the valves on both the oxygen and the acetylene tanks. The valves on the torch itself should be closed. Adjust the tank valves to the desired pressure. Wait a few minutes to ensure tank pressure does not drop because of possible holes in the gas lines.
Open the acetylene valve on the torch slightly and ignite with the sparker.
Open the acetylene valve a little more until the bright yellow flame stops smoking. The flame should be less than a foot long.
Open the oxygen valve on the torch slowly; the flame should become smaller, more focused and bluer. Stop adding oxygen when you notice a small white flame forming at the tip of the welder's nozzle.
Turn off the oxygen at the torch before the acetylene when you wish to shut the welder down, followed by the valves on the two tanks.