Supersets are good if you want to increase the intensity of your workouts. They aren't necessarily better than a single set; it depends on what you're going for. Use the search function and I'm sure you can find lots of older posts about supersets. Or just use Google.
Here are some supersets I enjoy:
Incline DB Presses + Incline Flyes or Pullovers
Arnold Presses + Rear Lateral Raises (or any other rear delt exercise)
Supersets work well with the same muscle groups (i.e., incline presses + flyes) and with opposing muscle groups (back exercise + chest exercise, ect..). Make sure to put the most difficult movement first.