Welding for the first time - need advice

FWIW, if you're trying to do sheet metal, get some heavier stuff to practice on first.

Also, with a Mig, I'd be surprised if you're going to lay a bead. It's more like a series of small tack welds (kinda like stitch welding) that eventually overlap. You'll tack it here, then way over there, and then over yonder away from the first two, and so on, so you don't build a lot of heat into the panel and warp it.