One easy way to construct a set is to draw a picture of it. A common way of doing so is a Venn diagram such as this one:
This diagram indicates that the setconsists of all of the points in the left-hand circle, while set consists of the points in the right hand circle.
Be careful: although Venn diagrams are a great way to create examples, they do not provide proofs that work for arbitrary sets. For example, an argument made using the diagram above does not describe the cases whereor when . Moreover, it doesn't consider finite sets or sets that are larger than any set of points in the plane. Venn diagrams give intuition (and examples) but not proofs.