The slip stitch is the shortest, simplest stitch in crocheting. Slip Stitches are used to move the yarn forward while still staying as short as possible. I use them mostly when finishing a piece to hide the end, as a border or design, and occasionally for sewing two pieces together.
These boxes are checkboxes
Like I said before, you can use slip stitches to join a chain and make a ring. Here I have 10 chs, and if I just sl.st into the first then I’ll have a ring!
You can also use them for joining in the round, another technique for crocheting in the round (one I don’t usually use)