This document discusses the use of definite and indefinite articles in English. It explains that "a" and "an" are indefinite articles used with singular nouns, and "a" is used before consonant sounds while "an" is used before vowel sounds. It also discusses the definite article "the" and when it is used to refer to something already mentioned or something unique. The document provides examples of the correct usage of "a", "an", and "the" and cases when they should not be used.