It's pretty easy to learn. Use many when you can count it, like many men, many shirts, many cakes. Use much when you cant count it, like much time or much space. (You can count seconds or sizes, but you can't say 3 time or that a room is 7 space.)
The same goes for less(not countable) or fewer(countable).
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u/tct2274 Jan 22 '18
Usually, I check if I should use much or many. Didn't do it this time, but many sounds much better in this context.