'how many' is an interrogative phrase used to ask about the quantity or number of something. It is used to inquire about countable items.
'how many' is used before plural nouns to ask about quantity. It is not used for uncountable nouns; for those, 'how much' is used instead.
How many apples do you have?
How many books have you read this year?
How many students are in your class?
remember to use 'how many' with countable nouns. For uncountable nouns like water, money, or information, use 'how much.' A common mistake is using 'how many' with singular nouns. For instance, 'How many book do you have?' is incorrect. It should be 'How many books do you have?' 'How many' can also be used in indirect questions
'I wonder how many people will attend the event.'