Help with a beginner Q: how to divide stitches from in the round to front and back?

I am attempting to make a Purl Soho Cap Sleeve Lattice Top:

I have converted it so i am now knitting in the round from the bottom up
I have never made a sweater before, and I am now realizing I don’t understand the mechanics of switching from knitting in the round to dividing the stitches in half to knit the front and back separately. Is it really just as simple as moving half the stitches onto waste yarn or do i need to do purl backwards to make it “flat” first? I tried looking this up and assume this must be something really obvious that I am missing, thank you!!

This pattern doesn’t seem to have any sts bound off at the armholes so, yes, divide the sts in half. Work across half the sts, put the next however many sts on hold, turn and purl back on the sts you’ve just knit then continue with the pattern.

Thank you! I am hoping it will make more sense where I get to that spot, I am so far a pretty basic knitter, never having put stitches on hold before it was making me nervous, thanks!!