The inverted pyramid is a formatting style used by journalists to construct their writing. The pyramid tackles the who, what, where, when, why, and how aspects of a story from facts of greatest importance to least importance.
The pyramid is useful because all the facts that a reader absolutely needs to know to understand the gist of a story can be found within the first couple paragraphs. This is efficient when a reader doesn't have time to finish the whole story or the story needs to be cut short to fit the paper.
The pyramid started around the time of telegraphs in the Civil War. Telegraph wires could lose power at any point, so stories were put in order of greatest to least importance incase the telegram cut off.