1、many修饰可数名词复数，如：There are many people.
much修饰不可数名词复数，如：I have much money.
2、many作代词代表可数名词，如：Many of the students have great results.
much作代词代表不可数名词，如：Much of the air is fresh.
3、much还可以修饰动词，many不行。如：I love you so much.
He's much taller than her.
It's much more difficult than you thought
Did you see many people there
Many poets have died young.
Do you have much money left
He doesn’t spend much time preparing his lessons.
Many housewives find it a tiring job to keep a house.
She hadn’t much money, but she felt very happy.