The slip stitch is an important hand sewing stitch to know.  It's perfect for closing up those holes you leave in order to flip a project right side out.  When done correctly, you'll never even be able to tell where the hole was or even be able see the thread.  This is not something that can be replicated with a sew machine and will become one of your most invaluable hand stitches.  In this demonstration I use a contrasting thread color so it'll be easier to see, but make sure you use a matching one so your stitches will be nearly invisible and won't affect the way your project looks.