Pattern help

I’m working on my first DPN project, mini mittens. I’m finished with the body of the mitten, but I’m not understanding how to make the thumb. The pattern states: Knit up 3 sts across bottom edge of purled sts on one needle, turn mitten upside down and knit up 3 sts across top edge of purled sts on a second needle. Working circularly, knit 3 rounds." Can someone please put this in elementary terms? Do I pick up sts on those purl sts? What does “knit up” mean exactly?
Thanks for your help!! :XX:

I think that knit up means the same as pick up and knit the stitches, and it seems to make sense, so I’d do that.