You use "much" with uncountable nouns (eg: time, water... ) or to modify a verb (for example "I love you much"), "many" with countable nouns (eg: books, desks... "I have many picture books"), use "more" to compare ("I have more stamps than my friend has" ) and use "very" with adjectives ("The exercise is very difficult") Sometimes, you use "much more" or "very much more" to emphasize a comparation.
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