There are two types of articles:the definite article (the) and the indefinite articles (a, an). The indefinite article is usually used
first to point out a noun such as a person or thing. By doing that, it doesn’t have to be clear about which particular person or thing is being referred to. When the same person or thing is mentioned again, the definite article the is introduced to indicate the person or thing that has already been mentioned.
Sometimes, not any one of the articles is used. Such non-use of the article is given the name zero article which is used to say that the zero article is used when no article is actually used. Having a clear understanding of the different articles enables the right articles to be chosen for use, for using an article incorrectly in a sentence conveys a different meaning from the one that is intended.
Firstly Article a is used before nouns that begin with a consonant.
Secondly Article an is used before nouns that begin a vowel or vowel sound (such as an hour).
Thirdly Article the is used for all nouns that have been mentioned earlier.
Articles are a kind of adjectives as they precede and modify the noun that follows them. Commonly, an article appears before a descriptive adjective that modifies a noun in a sentence as the following examples show.