Another way to change the number of stitches on the needle is to increase. Like with decreasing, there are several kinds of increasing; some are visible, and others blend completely into their surroundings.
One of the most common variations is the bar increase, which is made by working in the front and back loops of the same stitch. It leaves a small, slightly visible bar (thus the name) on the right side of the work. This bar can either be hidden in a seam or used as decoration.
bar increase 
inc 1 st
The bar increase is a visible increase. A horizontal bar will follow the increased stitch on the knit side of the work, whether you work the increase on the knit or the purl side.
1. To increase on the knit side, insert the right needle knitwise into the stitch to be increased. Wrap the yarn around the right needle and pull it through as if knitting, but leave the stitch on the left needle.
2. Insert the right needle into the back of the same stitch. Wrap the yarn around the needle and pull it through. Slip the stitch from the left needle. You now have two stitches on the right needle.
working in front and back loops
Knitting into the front loop
Knitting into the back loop
Purling into the front loop
Purling into the back loop