If you want to change the width of your knitting you will need to learn how to increase and decrease stitches. This will allow you to make more interesting knitted shapes.
When you increase stitches you are adding an extra stitch (or loop) to your needle. This will increase the length of your row by 1 stitch, thus increasing the width.
When you decrease stitches you are removing a stitch (or loop) from your needle. This will shrink the length of your row by 1 stitch, thus decreasing the width.
I suggest using wooden needles when learning how to knit.
For more knitting lessons check out this guide.