The internet has many sites to explain countable and uncountable nouns.
Countable nouns are individual objects, people, places, etc. which can be counted. Nouns are considered content words meaning they provide the people, things, ideas, etc. about which we speak. Nouns are one of the eight parts of speech.
books, Italians, pictures, stations, men, etc.
A countable noun can be both singular - a friend, a house, etc. - or plural - a few apples, lots of trees, etc.
Use the singular form of the verb with a singular countable noun:
There is a book on the table.
That student is excellent!
Use the plural form of the verb with a countable noun in the plural:
There are some students in the classroom.
Those houses are very big, aren't they?
Uncountable nouns are materials, concepts, information, etc. which are not individual objects and can not be counted.
information, water, understanding, wood, cheese, etc.