Front Border of a Cardigan

I’m working on the border of a cardigan. The pattern reads:
cast on 1 st (this st to be used to sew border to front) and knit across 6 sts left on a stitch holder

I have the 6 sts on the holder. But am I casting on that “cast on 1 st” from the ball of yarn? Is that cast on stitch on the left hand needle? I don’t understand how to knit across the 6 sts on the holder. Is the stitch holder the right needle now?

Cast one st onto the working needle with a new end of yarn (or if you’ve left some working yarn with the 6sts on the holder, use that strand). Put that needle into your right hand and with the stitch holder in your left hand, knit the 6sts off the stitch holder. The one stitch cast on won’t be connected to the other sts until the next row, but that should be ok.

Thank you!