Both of these decrease methods are used in the sock pattern. One creates a decrease that leans to the right; the other leans to the left.
Knit Two Together
This technique can also be used for the purl stitch.
1. To create this right leaning decrease, knit 2 stitches, rather than 1, at the same time, as shown.
Slip, Slip, Knit
2. To create this left-leaning decrease, slip 1 stitch from the left to the right needle as if you were going to knit. Repeat with a second stitch (a). Then, insert the left needle into the front of the two slipped stitches (b), and knit them together.