1. Take two people with a common ancestor.
2. Put the name of the closest common ancester in the box marked common ancestor.
3. Put the name of the first person on the left in the box marked with that person's relationship relative to the common ancestor.
4. Do the same for the second person.
5. Where the two rows meet is the how the two people are related.
Example:
Cousins. Closest common relative is grandmother/granfather. One person goes in the grandson/granddaughter box on the left. The other person goes in the grandson/granddaugher box on the right. Where the two rows meet it says 1st cousins.