Step 9: Weld!
Jam down on the foot-pedal to quickly dump a bunch of current and heat into the metal.
The idea is to very quickly heat the metal and start the weld pool. You'll know it when you see it - the metal becomes fluid.
Start on an edge.
When the pool has formed, touch the rod in.
If you heat the metal for too long, it will warp. The longer the metal is heated, the more it will warp.
This is a "tack" weld, to hold the metal piece in place, so you can take off the clamps and do big long bead welds.
Once you have a weld pool started, you can ease off the pedal a little, to control the amount of heat and current being applied to the metal.
Welds shrink as they cool, so you can alternate sides to keep the welds even, and to keep one side of metal from getting too hot and warping. Hot metal can warp a great deal, and if you don't change sides, you might find yourself even 1/4" off of where the metal ought to be.