-So start with the stitches on your working needle. For your first row you will slip (as if to purl*) the first stitch onto your empty needle without knitting or purling it, just slip it from one needle to the other. Then purl the remaining stitches.
-For the second row you are going to slip that first stitch (as if to knit), then knit the second stitch. The third stitch you will slip as if to purl. *Which means look at this third stitch as if you are going to purl it but instead of purling it just slip it from one needle to the other. Repeat, odd stitiches will be slipped stitches (as if to purl) even stitches will be knit, to the end of the row.
This is different from slipping as if to knit because your needle will be in a different position, but it is still a slip stitch. Does that make any sense? I know the first time I read those instructions it took me 10 minutes to figure out what that meant. But I had to switch my yarn around and slip in a different way. As you move along with the heel flap you will see that by slipping as if to knit and then purling your yarn goes almost around that slip stitch and you are reinforcing the heel a bit so it can take more wear.
-For your third row repeat row one
-For your fourth row repeat row two
You are going to alternate these two rows, over and over until you have 2 inches of heel flap worked. End with a knit/slip row as your last row worked.
I will take a few more pictures of this step with my next pair of socks so that it is really clear.