When you knit with two needles you can put the thread or the wool around your needles in different ways, so that you get different patterns in the wool. So in this picture for example, you have two different stitches. The one on the left is called "rib stitch" and the one on the right is called pearl stitch. Yesterday I started to knit a scarf for myself. The wool is dark green and it's in rib stitch. Until today I've knitted four balls of wool, but I think I will need ten all together, because it is going to be a very big scarf to help keep me warm this winter.