Use many when describing count-nouns; use much when describing non-count nouns.
Knowing the difference between a count-noun and a non-count noun (also called a mass noun) can be a little tricky . . .
Basically, count-nouns describe things that are countable (can be counted), such as rocks, clouds, stars, cats, words, and people. And non-count nouns are not countable, like water, air, fire, and love. Count-nouns use many and few / fewer, and can be pluralized. Non-count nouns use much and little / less:
How many people are coming to the party?
How much alcohol will be at the party?
We only have a few minutes to talk now.
We only have a little time to talk now.
Please try to make fewer mistakes.
Please try to do less evil.
There are some complexities here….
The difference between a count noun and non-count noun is not perfectly based on the meanings of the nouns. It is simply a grammatical property. A count-noun is something we talk about as if it were countable. Same idea for non-count nouns. But some nouns can go either way, with different meanings:
How much water did you drink?
How many waters (glasses of water) did you order?
How much freedom do people have in North Korea?
How many freedoms are listed in the US constitution?
In general, anything that can be counted will be a count-noun, while substances and abstract ‘things’ (like love, honor, and freedom) will be non-count nouns. But examples of abstracts, and kinds of substances are count-nouns:
How much love do you feel?
How many loves (people loved) have you had?
How much wine did you drink?
How many wines (kinds of wine) do they sell?
How many wines (glasses of wine) did you order?
Remember that nouns are never pluralized after much and always pluralized after many.