Much se usa para describir una gran cantidad de algo, many describe un gran número de cosas.

El uso de much y many   much mucho (singular!)   many muchos, muchas (plural!)

Ejemplos     I haven't got much time to wait for you again!   They have many friends in your town?   Eat as much as you like!   There are just too many people around; I cannot find Peter among them.   Much has happened during the last year.   Many people have left already for the day, because of the nice weather.