There are 4 worlds to complete. USA, Mexico, France, and Japan. They are done in that order. Each world consists of 10 levels with the last always being a boss. You defeat the bosses by completing burgers much like any other level. Each time you finish a burger the boss will eat it and lose some health. The USA and France bosses take 3 burgers to defeat. 5-6 for the Mexican boss and 4 burgers for the Japanese boss.