Some English learners use the word "much" too much! In normal conversational English, "a lot of ___" is far more common than "much ___":

There was a lot of dust in the air.

My daughter always likes to put a lot of ketchup on her fries.

However, you can use "much" when you're saying "not much":

There's not much money left.

And it's good in the phrase "too much":

Sorry, I can't. I have way too much work to do here.

You can also use "much" for very, very formal positive sentences. When I hear a sentence like this, it reminds me of the Bible! It has that level of formality and age.

There was much rejoicing among the people.

"Many" is the same as "much". It sounds strange and old-fashioned in positive sentences, but normal in questions and negative sentences.

There were a lot of people there.

There aren't very many chairs left.