Get some stock to practice on that’s the same stainless type (if you don’t know, get some 302) in the exact same thickness. The main issue for new players in Stainless and mufflers is that that thin wall tube goes up in smoke really fast. You’ll blow through if you’re not careful, but you need 100% pen to get strength out of the joint so it’s a balancing act. The other hard part is welding on a round. If you’ve only welded flat, try welding out of position on thin stuff and you’ll see why people charge good modey for it lol.
Look up “sugaring” and see make sure you work on getting your regulator setup so that you have complete argon coverage both sides of the joint. Also, just a heads up, if you set the second regulator pressure (flow rate) too high they you’ll blow out your welds. You want a really low flow rate like ~5CFH max.