What does the law of superstition tell about the relitive age of rocks

If you were referring to the law of superposition then this law explains that when rock layers are undisturbed, the layers that form on the very top are younger than the layers that formed below it.  We say undisturbed because other events can change the arrangement of layers like a fault.

This law was first proposed by Nicolas Steno, who came up with the 4 principles of stratigraphy.