There are two kinds of Articles. They are–
  1. Indefinite Article – ‘A’ or ‘An
  2. Definite Article – ‘The
Indefinite Article (A/An) shows indefiniteness and Definite Article (The) shows definiteness.

kinds of articles

Articles (A, An, The) are used before Nouns under some rules. When a Singular Countable Noun is used for the first time, Article ‘A’ or ‘An’ is used before it. But when a Countable Noun, whether Singular or Plural, is used for a definite thing, or refers to a thing or person that has already been referred to earlier, Article ‘The’ is used before it. Thus when a Singular Countable Noun is used for the first time, Article ‘a’ or ‘an’ is used before it, but when the same noun is repeated in the same sentence or in the subsequent sentences, Article ‘The’ is used before it because then it becomes a definite thing already referred to earlier. As –
  1. I have a book. The book id very informative.
  2. I have a book, though the book is not very informative.
  3. There was a house. The house was very large.
  4. There was a house and the house was very large.
Note:
    Singular Indefinite Noun           –  A or An
    Singular/Plural Definite Noun  –  The