If you’re MIG welding (and you should be) you’ll need to buy or rent a welding gas cylinder from your local welding supply shop. For MIG welding steel, a 75/25-percent mix of Argon/CO2 is the most common. You can MIG with 100-percent CO2, but you’ll have to buy an adapter to work with the supplied Lincoln regulator. Spin the knob to set the flow rate. Specs in Lincoln’s instruction sheet call for 30-40 cubic-feet per hour, but we normally run 20-30 cubic-feet in the garage and only up the gas rate if we’re welding outdoors or out of position.