All common nouns are either countable or uncountable. ' Countable nouns" are those nouns which we can count. ( one, two, three, etc.). Countable nouns are mostly in singular and plural forms. The singular form can use determiners a/an.
' Uncountable nouns' are those nouns which cannot be counted. ( some, much, little). They may be names for abstract ideas, qualities or physical objects that are too difficult to be calculated, for ex: liquids, gases, or solids like sugar, grains, milk, air etc.
We cannot use a/an with these nouns. To express the number of uncountable nouns use words or expression like - some, much, little, or we can also use exact measurements - a cup of, a bag of, a handful of, a pinch of, an hour of. If you want to about the quantity of an uncountable noun, you can ask - How much.