ARTICLE

A. Indefinite article:
    A:
          Is used with words that start with a consonant.
Examples:
    A boy.      A pen.     A teacher.
          Is used with countable and singular nouns.
Examples:
    A table.    A student.
           Is used when the person or thing is undefined and unspecific.
     An:
            Is used with words that start with a vowel (a-e-i-o-u).
Examples:
      An orange .    An actor.     An engineer.
             Is used only with countable and singular nouns.
             Is used when the person or thing is undefined and unspecific .
B. Definite article. 
     The:
            Is used with both singular and plural nouns .
Examples:
       The boy.         The boys .
             Is used with both words that start with a consonant and those that start with a vowel.
Examples:
      The orange.           The student.
            "The" is a definite article used when the thing or the person is defined and specific.