yup, circulars are just used for flat knitting a lot. They hold a lot of stitches, they are more ergonomic because the knitting lies in your lap easier (and doesn’t require so much motion).
I DO NOT own any straight needles (that are not horribly wrecked and beyond any use). I only knit everything on circulars and double pointed needles.
the description you already have:
cast on your stitches. work them off from the end that the cast on puts you to. turn your work and work back: you work the stitch first that you just worked last.
This is no knitting in the round because you do not join the ends.
this is not magic loop - in magic loop you basically knit something on circulars that is a lot smaller than the cord of your needles.
and the circulars are just a replacement for straight needles.
I do not know how you piece continues, but at least for now you can work on straight needles if you really want to.