PM = Place Marker
Again I knit toe-up so bear with me.
Needle one and three should hold your heel and gusset stitches and needle 2 your instep (top of foot) stitches. When you reach the end of needle 1 you will knit until there are three stitches left on the needle. Knit together (K2tog) the third and second stitch for the last and then knit the last stitch. You have begun to close the gusset. knit across needle 2, on needle three knit the first stitch and then knit the next 2 stitches together (K2tog). Knit the remaining stitches on needle three. Next round knit all stitches.
Repeat these two rounds until all gusset stitches have been knit and there are 44 stitches remaining on all needles.
Again you might want to review the video on turning the heel
Don't worry after you first sock is just gets easier and more addictive.