Countable Nouns vs Uncountable Nouns

UnCountable Nouns
A countable noun is the name of anything that we can count in both the singular and plural forms. The opposite of countable noun is the uncountable noun and the collective nouns.
For example: The boys helped to keep the toys after playing
Uncountable Nouns

An uncountable noun also called the mass noun is a noun that does not have a plural form which you could not count. An uncountable noun always take a singular verb (is, was) in a sentence. Uncountable nouns are similar to collective nouns and are the opposite of countable noun.
For example: The air is fresh and the sand is pearly white. (since air and sand are uncountable, is (verb) is used even if we are refering to abundant of air and plenty of sand.
Note: Both countable and uncountable nouns are concrete nouns.
Nouns that can be made countable and uncountable
I borrowed this from a website for its clear explanation
Sometimes, the same noun can be countable and uncountable, often with a change of meaning.

Countable Nouns	Uncountable Nouns
There are two hairs in my coffee!	I don’t have much hair.
There are two lights in our bedroom.	Close the curtain. There’s too much light!
Shhhhh! I thought I heard a noise.	It’s difficult to work when there is too much noise.
Have you got a paper to read? (= newspaper)	I want to draw a picture. Have you got some paper?
Our house has seven rooms.	Is there room for me to sit here?
We had a great time at the party.	Have you got time for a coffee?
Macbeth is one of Shakespeare’s greatest works.	I have no money. I need work!

Note: Drinks are uncountable but if we wish to order a cup of coffee or 2 glasses of orange juice we can say “one coffee and two orange juice please”.