Who the Hell Is This Person Talking to Me and How Exactly Are They Related to Me: The Chart, just in time for your Thanksgiving gathering.
(Source: Apparently commenter “Platypus Man” from this Lifehacker post)
Oooh! I really like that this chart gives (average) percentage of genetic similarity.
And confession: Despite my genealogy hobby, I can never remember what my cousins’ children are called in relation to me. (First cousin once removed, apparently.)
Most genealogy programs also include features that will show relationships between selected persons. Check your user guide to learn how to use it.