Countable nouns are the words for things that we can count. Countable nouns have singular and plural forms. Examples are: boy, boys, girl, girls, flower, flowers, book, books, chair, chairs, student, students etc.
A singular countable noun requires an article or another determiner (e.g. the, my, this etc.) with it.
I ate an orange. (NOT I ate orange.)
She put the book on the table. (NOT She put book on table.)
Would you like a piece of cake?
Where shall I put my coat?
Uncountable nouns are the words for things that cannot be counted. Uncountable nouns cannot be used with a/an. Also, they do not have plural forms.
I would like some advice. (NOT I would like some advices.)
Have you got any information? (NOT Have you got any informations?)
Mix the water with the flour.
Here are some examples of common uncountable nouns: advice, air, anger, beauty, behavior, damage, furniture, happiness, homework, information, meat, luggage, progress, safety, money, knowledge, water and work.
You have to be careful with uncountable nouns because they can be countable in your language. Remember that uncountable nouns are considered as singular and hence they should be followed by singular verbs.
The meat has to be cooked properly.
The information that we received from him was not correct.
Your rude behavior upsets everyone.
