Countable noun refers to anything that you can be counted. It includes animals, persons, places or things. Here are some examples: Fish, soldier, pencil.
Uncountable noun refers to things that cannot be counted. Uncountable nouns are mostly intangible things. They include things like emotions, character traits and ideas.
Examples include: Joy, happiness, love, flour and rain.
Countable and uncountable nouns can be in singular or plural forms. In the singular form, the noun is preceded by 'a/an'. Uncountable nouns can be used alone but it can also be used along with words like: much, some,a little and any.
Example: Mary had a little sleep.
Some nouns can be countable or uncountable, it depends on how it is used in a sentence. Examples- time, light, hair and do much more.