If you need steel to practice on, Tri-Star steel (9821 Freeland St in Detroit) is a great source. They let you walk around and sort through their scrap piles/bins and load up the scale with as much as you want for around $.20/lb which is cheaper than anybody else around that I know of.
Get some .25" thick plate 6x9" (ballpark) and make a pad of beads with it. Run a continuous bead all the way from end to end, then start another bead and overlay it 1/3 of the way over the bead before it. Every couple of beads dunk the pad in water to cool it off (when it gets hot it acts like you're increasing the amperage). By the time you've got the pad covered you'll have a much better idea of how things work.
If you can switch to a bottle you'll probably be happier. I've even bought a used bottle off Craigslist that came from a local welding supply place, so they didn't give me a hard time about where it came from, or when it was inspected last...and I think I only paid $100 for it (biggest 100% argon bottle size I've seen).