When we use a noun countably we are thinking of specific things; when we use it uncountably we are thinking of stuff or material or the idea of a thing in general.
Here are some more nouns used in both ways. Make sure you know the difference between the uncountable and the countable meaning.
drink / a drink hair / a hair paper / a paper land / a land
people / a people home / a home policy / a policy trade /a trade
Drink was the cause of all his problems, [alcohol]
There’s a hair in my sandwich, a dark one; it must be yours.
Did you buy a paper this morning? [a newspaper]
I love meeting people from different countries, [individuals]
The different peoples of Asia, [races / national groups]
Her grandmother lives in a home, [an institution]
I’ve lost my car insurance policy, [a document]
Trade with China has increased, [imports and exports]
The names of food items often have a different shade of meaning when used countably and uncountably (see fish above).