To turn a heel, you have to work short rows, meaning that you aren't working across all the stitches in a single sock's heel on every row. That means when you're working socks two at a time, you have to complete one heel turn before you can start the other.
If you're following a pattern, it will give you the math for the heel turn, but if you're working the sample socks, the heel is turned as follows:
- Row 1: Slip 1, knit 5, knit 2 together, knit 1. Turn.
- Row 2: Slip 1, knit 3, slip, slip, knit, knit 1. Turn.
- Row 3: Slip 1, knit 4, k2tog. Turn.
- Row 4: Slip 1, knit 4, ssk.
Once the heel has been worked, pick up and knit stitches along the left-hand side of the first sock's heel flap.
Adjust the needles as necessary to do the same thing on the second sock. Leave the second half of the heel flap without having picked up the stitches for now.
