What is the difference between countable and uncountable nouns?

Question

Countable nouns include words like an apple, two apples, three apples, etc. Uncountable nouns include words such as air, rice, water, etc. 

Answer 1

Nouns can be countable or uncountable. Countable nouns can be counted, e.g. an apple, two apples, three apples, etc. Uncountable nouns cannot be counted, e.g. air, rice, water, etc. 

Example sentences:

Countable: I have three apples.

Uncountable: Would you pass me the water?