The Slip, Slip, Purl stitch is commonly used during the heel turn of various types of heels. It's not quite as intuitive as it seems - you need to work the purl part from the back. Take a look.
by Whiletheyplay
by Red Heart Yarns
by planetpurl
by PurlSoho
by KnitItOut Vancity
by KnitFreedom
by Patty Lyons