The difference between "how much" and "how many"
If you want to know the amount (= Menge, Anzahl) of something you can ask a question starting with "how much" or "how many".
How much is always used with uncountable nouns (unzählbaren Nomen/Hauptwörtern).
Example: How much milk do you need?
You also use "how much" if you want to know the price of a product.
Example: How much is this T-shirt?
"How many" is always used with countable nouns (zählbaren Nomen/Hauptwörtern).
Example: How many pupils are in the classroom?