Much means “in large degree or quantity.”
Many means “numerous” or “of an indefinite number.”
Generally, much is applied to mass nouns and things that are not easily quantified, and many is used for groups of singular nouns that have not been accurately counted, but could be.
Much also modifies both nouns and verbs while many applies only to nouns.
Example: We don’t like to use much salt, but not many people do.