Countable nouns

English nouns are often diveded in "countable" or "uncountable".

Countable nouns are things that we can count.

For example: "pen", we can count pens. We can have one, two, three or more pens. Here are some more countable nouns:

Ex: dog, cat, animal, man, person

Countable nouns can be singular or plural:
Ex: My dog is playing.
Ex: My dogs are hungry.

We can use the indefinite article a/an with countable nouns:
Ex:A dog is an animal.

When a countable noun is singular, we must use a word like a/the/my/this with it:

Ex: I want an orange. (not: I want orange.)
Ex: Where is my bottle? (not: Where is bottle?)

Uncountable nouns

Uncountable nouns are substances,
qualities, processes, concepts, etc... that we cannot divide into separate elements, we cannot "count" them.

These nouns have only one form,
are not used with numbers, and are not usually used with the determinants, ”the”,
”a” or ”an”.

Ex: money, paper, water, salt, milk, education, energy


Quantifying uncountable nouns

Uncountable nouns can be quantified using expressions such as: little, much,
some, kinds of, types of etc., see above.

Ex: time (little), treatment (kinds of), advice (some)

Credits:

http://www.learnenglish.de/grammar/noununcount.htm
http://www.britishcouncil.org/learnenglish-central-grammar-nouns-uncountable.htm