This somewhat simple rule can become very complicated when either or both parents have multiple marriages or relationships. At this point, it is important for the researcher to understand how people can be related. There is a basic tutorial consisting of a series of lessons in the Family Tree Training Lessons and Videos that can be very helpful. This series of lessons starting in Level One and continuing in both Level Two and Level Three can help you to understand and advance your knowledge of the program. You should always work your way through all of the preceding lessons. This series begins in Level One with learning to use the "Sandbox." The Sandbox is a practice or dummy example of the Family Tree program that can be used without making changes to the actual program. Learning to use the Sandbox will enable you not only to learn the more involved parts of the entire program, but can also be used to teach others about the program without the danger that data in the "live" version of Family Tree will be lost.
Here is a screenshot of the Level One Sandbox Instruction location: