How do I finish this seam?

by Shawntel
(US)

I am working on a 5 hour sweater. I am working on the sleeve and it says bind off on the bottom of the sleeve leave one stitch on needle and slip stitch back up I am confused. I have bound off and left the one stitch on my needle. How do I get this seam closed PLEASE HELP (The pattern is a 5 Hour sweater for a baby boy.)