This tutorial shows how to increase using “knit front and back”. This is often abbreviated as kfb, and increases by one stitch knitwise. Increasing stitches will make the piece of knitting wider.
How to work a kfb increase
Your pattern will tell you where the increase will be, so you would knit to the point of the increase. In this example, I have 9 stitches on the needle before working the row. The instruction for this row is:
k1, kfb, knit the remaining stitches (10 stitches)
So I have knit the first stitch on the left needle, and I am going to increase into the second stitch as follows:
STEP 1 - Knit the next stitch on the left needle, but do not slip the original stitch off the left needle.
STEP 2 - Insert the tip of the right needle into the back of the same stitch on the left needle.
STEP 3 - Pass the yarn under and around the tip of the right needle (as you would when knitting a stitch).
STEP 4 – Bring the right needle and the yarn wrapped around it through the stitch on the left needle. Now slip the original stitch off the left needle, and the increase is complete.
Remember, I had 9 stitches when I started knitting this row. After the increase, there are 10 stitches (three on the right needle and seven on the left needle). So the kfb has increased the number of stitches by one stitch.
I have continued to increase at the beginning of each knit row in my sample, and you can see that the edge is sloping where the increases have been made (on the right hand side of the picture).
The sample has decreases at the bottom (sloping like this \ ) and increases at the top (sloping like this / ).