We have the same info. With the yarn in back of working needle, Slip first st as if to purl (your needle goes in front leg of stitch from right to left then stitch is moved to right hand working needle), bring yarn to front of fabric, then purl one stitch, move yarn to the back, then slip one st from left to right hand needle as if purling, etc. I'm right-handed and holding working yarn in right hand, stabbing and wrapping.
Round 4 starts with a purlstitch then a slipped stitch whereas Round 2 starts with a slipped stitch then a purl stitch. Location of Slipped stitches alternates between rounds 2 and 4.
Rounds 1and 3 are purl rounds.