How Do I? Please Help

I am knitting a pattern from called Roving - Houndtooth Pillow. In the instructions it says

“With A, P1. *Insert right hand needle from behind under running thread between the st just worked and next st, then purl this thread.”

What does that mean? How would I do that? Margie:knitting:

It may be easier to put the left needle into the strand between the sts and purl it.