How to crochet a slip stitch ( sl st)

If you're just starting crochet, the slip stitch (sl st) is one of the first techniques you'll learn and one of the most useful. A slip stitch is the shortest and simplest stitch in crochet.
It doesn’t add height like other stitches; instead, it’s used to join rounds or pieces, finish edges neatly, and create sewn patterns in a shape. 

Below, we will go through the steps to use the slip stitch along the edge of a pattern and to create a pattern on a piece. 

On the edge of an open piece 

To make a slip stitch at the edge of a piece, insert the hook into the next stitch. You see 3 loops on the hook at this step. 

Now, yarn over and pull the yarn through all 3 loops on the hook to be left with just one loop on the hook. This is basically a shorter version of a single crochet stitch since you are directly pulling the yarn through both the stitch on the piece and the loop on the hook. 

Congratulations! You created your first slip stitch (sl st).

After a few in a row, you can see how they don't add any height and only add a more refined end on the edge of the piece. 

A design on a piece

 To slip stitch a design on a piece, first, we need to create 1 loop on the hook to start crocheting that into the main piece. You can use the same method as making a chain in this article here. 

Once you have 1 loop on the hook, insert the hook between 2 rows on the piece. The goal of this piece is to create accent lines from the bottom to the top. Pull the yarn coming from this loop on the back of the hook. This will position the working yarn better and help you secure the short yarn tail with your finger, making it easier to start. 

With the hook inserted in the body and the yarn in working position, yarn over and pull it through the piece and the loop on the hook together. 

This creates the first slip stitch into a piece. You should see what looks like 2 stitches on the piece: the first is the loop you started with on the hook.