Kitchener Stitch, or grafting, is used to join two sets of live stitches together. You'll see it used in socks, scarves that have a symmetrical lace pattern, the underarms of seamless sweaters, and some cowls.
I'm sure there are knitters who can graft without having to check their knitting books or google "kitchener stitch" but I am not one of them.
So I made myself a little cheat sheet, printed off a few, and put one in every knitting basket. And I thought, hey, other knitters might like this too! Here's a free pdf for a Kitchener Stitch cheat sheet; just print it on letter size paper or card stock, and cut it along the crop lines.