The most commonly used decrease is created by knitting two stitches together:
The most commonly used decrease is created by knitting two stitches together: it is most generally written as K2tog. The two purple colored stitches are the two stitches that were knitted together. The yellow colored stitch that is on the needles is the newly formed stitch.
Instead of putting the working needle in the next stitch on the left needle, put the needle first in the second stitch on the left needle and then the first stitch on that left needle; knit these towo stitches together.