A noun is a word for a person, place, thing, idea, event, etc.
Like in English, nouns in French may be common or proper, count or mass, and singular or plural. Unlike English, French nouns are also either masculine or feminine.
Common nouns in English and French are the generic term for something. Common nouns never begin with a capital letter unless they begin a sentence.
une fleur a flower
Proper nouns are specific names and therefore, begin with capital letters.
Anne est à la Tour Eiffel. Ann is at the Eiffel Tower.
Another way to classify nouns is according to whether they can be counted or not. Count nouns identify individual identities that can be counted, like books.
un livre, deux livres a book, two books
In contrast, a mass noun refers to something as an uncountable