A LOT OF - MUCH - MANY

• A lot of :
  
  
  • A lot of can be used in all sentences: affirmative, negative and interrogative.

• Much - many : 
  
  
  • Much and many are used in negative and interrogative sentences.
        They are rarely used in affirmative sentences, except if they begin
        the sentence . (see below)
  • Much is used with uncountable nouns (for example: 'much English')
  • Many is used with countable nouns (for example : 'many words').

Affirmative	Negative	Interrogative
We learn a lot of English.	I don't know a lot of English.	Do you learn a lot of English?
I make a lot of mistakes.	I don't know much English.	Do you know much English?
BUT :
Much of our food is exported.	I don't know a lot of words.	Do you make a lot of mistakes?
Many people drive too fast.	I don't know many words.	Do you make many mistakes?

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Compare a lot of and a lot :

• Tom knows a lot of vocabulary.
• Charlie is talkative. He talks a lot.