Apparently I have to use a 3 thread stitch, not using one of the upper needles. I'll start practicing with that now.
I'm not that excited about the manual that came with the machine. I'm sure the info is in there somewhere, but it's not that easy to find; it doesn't seem to be for real beginners. However, I frequent my local used bookstores and got a couple of books - one is for beginners and one claims to have more advanced 'couture' techniques. (I haven't fully explored that one yet.)
You often find things in used books, as well as written-in notes from previous owners. It's one of the things I like about them. The beginner's book contained a yellowed folded paper sheet from Butterick, of all places, that was a handy quick reference even though it isn't about my machine. (It actually doesn't say what machine it does refer to, and the internet doesn't mention a serger/overlock made by Butterick, although they do seem to make sewing machines that may also serge.) This, and the book itself, supplied better guidance about what/where to explore.
So, more fun. I know I'm being ridiculous about not wanting the first trial to fail. It's not really fabric for a garment I could wear for anything but a work shirt. But I don't like to do 'muslin' trial garments that just get thrown away. I usually do something from fabric that isn't as special as the one I plan to end up using but still makes something I can use. It's just something that wouldn't break my heart if I did have to throw it away.
If I ruin the two fabrics that I plan to use eventually, I'm going to be 'sum pissed'. Old knit sheet, not so much. Just keep thinking that.