The slip stitch, or "sl st" as it is commonly abbreviated, is one of the most basic stitches in crochet. It can be used to work a row without adding any height, to close or complete a round, or to join to pieces (such as granny squares together). It is simple to do and can be worked quickly.
Here we'll work our slip stitch on a row. Begin by inserting your hook into a stitch as shown below,
Wrap the yarn around the hook,
Pull through the first loop in the hook, it will now look like the photo below:
And finish by pulling that loop through the other loop, it should now look like the photo below:
There you have it, the slip stitch!
Click below to watch a video on how to work the slip stitch: