To make a Venn diagrams, draw a rectangle that contains two or more overlapping circles, which are used to compare and contrast different groups of things, sometimes called "sets." Each circle should contain unique properties, while the overlapping section of the circle should contain properties the items have in common. For example, a Venn diagram comparing whales and fish may have "lives in water" and "have fins" in the middle, while "mammals" would only be in the circle about whales.
A Venn diagram is useful to determine what the relationship between sets of objects might be: for example, a Venn diagram comparing prime numbers and odd numbers between one and 10 would have significant overlap, since one, three, five and seven are both prime and odd, while the prime circle would only contain two and the odd circle would only contain nine. Using this Venn diagram, someone would then be able to determine that most odd numbers between one and 10 are also prime.
Adding a third circle to a Venn diagram allows for even greater specificity when determining properties: a third circle that contained even numbers between one and 10 would have no overlap with the circle of odd numbers, but it would share the number two with the prime numbers circle.