How to Knit Slip Stitch
It is often necessary to slip (sl) a stitch from one needle to the other without actually knitting or purling it. This method is often used in shaping or within a stitch pattern.
The pattern will usually specify whether to slip the stitch knitwise (as if to knit) or purlwise (as if to purl). If it does not say, slip the stitch purlwise. The working yarn should be held behind the work in both cases unless the pattern specifies otherwise.
Slipping the stitch purlwise
Slipping the stitch purlwise is where the right needle is inserted into the next stitch on the left needle as if to purl, but with the yarn still in back of the work. Instead of purling it, transfer the stitch to the right-hand needle. This method is used when the stitch is worked on the following row.
Slipping the stitch knitwise
Slipping the stitch knitwise is done by inserting the needle as if to knit and then transferring it from the left-hand needle to the right-hand needle without knitting it. This method causes the stitch to be twisted, which can become a feature of a stitch pattern.