Toe up sock question

[Jan in CA]

In this pattern at the toe cast on part:
http://www.wiseneedle.com/knitpatksox.asp

It says:

• Take a third dpn and knit across the top needle. Take the fourth dpn and knit across the bottom needle. Be careful not to twist stitches - one needle's loops will be "backward" with the leading edge of the loop on the rear side of the needle. Make sure you knit into the rear side of these "backward" loops.

I haven't quite figure out how to knit across, but my question is how to knit into the rear side of the backward loops. How do I tell which are the backward loops and then how do I knit into the rear side of them? Would I go down as if to purl or up as if to knit?