knitting, like driving a car, or touch typing, or lots of other tasks, is TWO HANDED.
there are 2 needles, (one goes in each hand!) and there is yarn (it can go in either hand!)
some lefties like a left hand yarn hold, some like a right.
when i teach, i teach how to hold and move the needles (and just leave the yarn hanging!)
when the student know how to move the needles, i say OK, now pick up the yarn and hold it in your hand as you work..
and they pick it up..
sometime right handed, some times left handed..
sometimes they change as they work.
eventually, they settle on which hand they want to hold the yarn in.. and then i teach how to purl!