Countable nouns are for things we can count using numbers. They have a singular and a plural form. The singular form can use the determiner “a” or “an”. If you want to ask about the quantity of a countable noun, you ask “How many?” combined with the plural countable noun.
Examples: bottles of wine, houses, people,
Uncountable nouns are for the things that we cannot count with numbers. They may be the names for abstract ideas or qualities or for physical objects that are too small or too amorphous to be counted (liquids, powders, gases, etc.). Uncountable nouns are used with a singular verb. They usually do not have a plural form.
Examples: wine, sand, air, money, knowledge.
When quantifying them one uses many for countable nouns and much for uncountable nouns (many houses, much wine, fewer people). For countable you use number and for uncountable you use amount (a large number of people, a great amount of sand, less tea).
So often now, people use amount when they need to use number. Two examples below
If you want to read more, here is a nice link