You knit til you have one stitch, then the gap from purling two together, then another stitch or two (however many are left). You purl together the one before the gap and the one after the gap. Leave whatever stitches are left after the gap after that, turn, and knit the other way til one before the gap from the last time you knit two together.
Watch the Knitting Help video on turning the heel of a sock. That sounded foreign to me too, but watching the video made it all clear.