How to read it
The banzuke is professional sumo's official ranking sheet. It lists every active wrestler from Yokozuna down through Jonokuchi, with referees and other personnel also appearing on the traditional printed version.
East and West are ranking positions, not teams or geographic conferences. When two wrestlers share the same numbered rank, the East position is normally considered slightly higher than the West position. Maegashira 3 East therefore sits just above Maegashira 3 West.
Why it changes
A new banzuke is prepared after each grand tournament and released before the next one. Winning records usually move a wrestler up, and losing records usually move one down, but there is no fixed points formula. The ranking committee must fit everyone's results into a limited number of places, so nearby records and open slots matter too.