For more practice, I cut some areas out of a piece of sheet steel, and tried welding in both a washer and a piece of bar stock with a hole in it, as those are the two ideas I have for restoring the bolt holes in the mower. This is how they looked when I was done with them.

That vertical piece of metal on the right was an attempt at doing what I saw someone do in a YouTube video: Just make a bunch of tiny welds and let them cool before going between them. I wasn't expecting it to work as well, and it doesn't look as good, but it did hold up to me beating it with a hammer.

Here's both sides of the washer:

...and here's both sides of the bar stock:

Overall there doesn't seem to be much to learn about welding, at least with this welder that I have. Like, you have to get the metal hot enough that the separate metals actually fuse, and because of that the wire has to feed at a certain rate, but you also have to not let it get so hot that it melts through, so you have to move at a certain rate. There doesn't seem to be any way of getting around any of that. So I don't see what I could learn to do better other than learn to move the welder in super smooth and straight motions.

Maybe a lack of flux is why gas welders are so popular. When I was looking at welders in YouTube videos, the kind that uses a gas but doesn't have a wire feeder seemed like the best kind, but I just went for the cheapest one, which is the kind that feeds wire that has a flux in it, so that it doesn't require any gas.

So I don't think there's much point in practicing anymore since I don't think there's anything to learn, and both that washer and that piece of bar stock seem to be quite attached to that sheet metal despite the welds kind of looking like shit, so I guess tomorrow I can work on fixing the mower.

Maybe I need a TIG welder if I want nice welds, but those things cost much more than a new lawnmower.

This guy seems to be using a TIG welder (unless there's some other kind of welder I haven't heard about) and does fairly well with it. Go to time offset 3:15 to see the welding.

...or maybe it's brazing? Though he says "weld" a lot, he also says "I melted my brazing way prematurely" which makes me wonder what exactly he is doing.