KFB, or knit front and back, is a commonly used increase stitch in knitting. This can also be referred to as a bar increase.
To do the knit front part, knit the stitch as you would normally but when you pull the loop through do not remove the old stitch from the left hand needle.
To do the knit back part, insert the tip of the right hand needle into the middle of the stitch on the left hand needle from right to left and bring the yarn around the right hand needle from back to front (as a normal knit stitch). Pull the needle back through with the new loop on it and slip the old stitch off the left hand needle.
Voila! One increase made!