Knit into the front and back is an increase. You knit into the front loop of the stitch as normal, but don't slide it off. Then knit into the back loop of that same stitch and then slide it off. You'll have two stitches instead of one.
K2tog is a decrease. Put your needle in through both the second and first stitches on the left needle in the direction you normally knit (so second stitch first), and knit them both at the same time.