What's the difference between "How many" and "How much"?

How many > Countable quantity of units or items
How much > intangible, commodity
How many kisses? How much love? How many loaves of bread? How much bread?
How much sunshine during the day? vs How many hours of sunshine during the day?

Many is used in situations where there are discrete items in the count, such as rocks, or people or cars. Much is used when there are no discrete items in the count, such as describing how much of a liquid or water or to express an idea like "confidence", etc...

eg:

How Many Rocks
How Many People
How Many Germs
How Many Minutes

How Much Water
How Much Confidence
How Much Time

How many usually means the amount needed for a certain task or a query as to the amount of things present during an event. How much usually is connected to the monetary value of something.