If you notice that crumbs appear on your little brother's shirt whenever the cookies disappear from the cookie jar, you can say that you've correlated two facts, meaning that you've established or revealed that they're linked in a way that explains both of them.
Detectives correlate pieces of evidence in order to solve crimes. For example, they might correlate a suspect’s bandaged hand with a shattered third-floor window. Correlate can also be used as a noun. Some companies promote products by suggesting that their products increase “happiness correlates,” or factors that have been shown to have a relationship with happiness, like health and friendship.