Articles a/an

1. Use “a”, “and” only with singular nouns

1.1. E.g. with "a" It´s a book                                       E.g. with "a" It´s a sharpener                              E.g. with "a" It´s a pencil

2. a|an are considered indefinite articles and they are used to introduce new concepts into a discourse.

3. Use “an” with words that start with a vowel sound

3.1. with "an" an elephant                                      with "an" an ant                                                   with "an" an alligator