A huge simplification of Vladimir Propp's Morphology of the folk tale.
In Morphology of the Folk Tale Propp deconstructed Russian stories to describe 31 plot elements or functions, e.g. The hero leaves home, the hero is tested, The hero acquires the use of a magical agent. Propp’s structural analysis, builds a formulae to read and recognise components in each tale. For example, citing a story about a Tsar, three daughters and a dragon, Propp describes an act of kidnapping thus: β³ð1A1B1CH1-I1 K4W°. The entire tale is a much longer set of symbols, the tale is condensed but patterns and similarities between stories are much easier to identify.
and here is a link of a slightly longer and more comprehensive explanation.