K2tog (knit 2 together) is a simple decrease used for shaping in knitting patterns.  You use exactly the same steps and technique as when you knit a stitch, except that you work into two stitches at the same time.

::: HOW TO WORK a k2tog :::

1) Insert your right hand (RH) needle through two stitches at the same time (from front to back).
2) Wrap the working yarn around the RH needle tip at the back of the work (exactly the same as you do when you knit a stitch), then use the RH needle tip to draw this loop from the back, through the 2 stitches, to the front, to create a new stitch on the RH needle.
3) Drop the two ‘old’ stitches off the LH needle.

Working a k2tog decreases the stitch count, because you have effectively gathered two stitches together into a single stitch.  If you work a series of k2togs (every other row) stacked on top of each other, you create a right-slanting line.

Similar decreases: k3tog (exactly the same, but working into 3 stitches at once)
Mirrored decreases: ssk or sl1-k1-psso (single left-slanting decreases)