For this case we use the question "how many" to refer to things that we can count numerically.
For example, we can say:
How many oranges are there?
How many numbers are between 1 and 10?
How many people are in the car?
We must differentiate this question from "how much". This last question we must use it for amounts that we can not count exactly.
For example, we can say:
How much orange juice is in the jar?
How much flour is placed in the food?