Learn how to decrease stitches by watching this helpful video. Although there are several ways of doing this, the easiest method for beginners is the "knit two together" technique.
This particular video was produced by the "KnitWitch" and it perfectly complements my illustrated step-by-step knitting instructions over
here.
The best way to learn is by having a go yourself. It doesn't really matter what size needles or yarn you have at this stage - it is more about learning the basics.
Why not watch this video a couple of times and then try to follow the step-by-step instructions?
You will be amazed how quickly you will pick it up.