When should you say 'How much...' and 'How many...'? First you have to know about countable and uncountable nouns. Countable can be counted just as they are. Uncountable nouns are tricky business to count because a unit of measurement is always required to gauge their quantity.
For example: 2 pens, 7 cars, 12 boys, 3 islands - these are countable nouns.
Now check this out: 2 jars of ink, 5 buckets of sand, 4 spoonfuls of sugar, 6 bowls of soup - I can't say 2 inks and 5 sugars so these nouns are uncountable because I cannot count them as they are; I need to use a suitable unit of measurement.
I made these countable and uncountable noun sorting cards, they focus on the use of 'how much' and 'how many'. We say 'How many...?' for countable nouns and 'How much...?' for uncountable nouns.