The top is worked in the round up to the armholes, with the exception of the drawstring casing at the hip. After the back is bound off, the rest of the front is worked back and forth.
The back ribbing is worked with a smaller needle while the front is worked with a larger needle, simultaneously. This technique is a little like knitting in the round with two circulars, and should be intuitive once you’ve started.
The drawstring casing may be a little challenging for some knitters. If you’d like an even easier knit, you can substitute the casing with a yo, k2tog round, then string the I-cord through the eyelets.