The slip stitch is almost a half-single crochet, and the both start the same way.
Insert your hook into the next stitch, yarn over and pull through. You now have two loops on your hook.
Instead of continuing a single crochet, draw the second loop (on the left) through the first loop (on the right).
That’s a slip stitch done!
I use this stitch for horizontal colour changes, and to finish of each open amigurumi piece. It makes the difference in levels between rows a little more subtle.