1. Definition of articles indefinite: According to the Oxford Dictionaries it is a determiner that introduces a noun phrase. a|an are considered indefinite articles and they are used to introduce new concepts into a discourse.
2. Example with"a": it's a butterfly
3. Rule: follow the following uses: Use “a”, “and” only with singular nouns Use “an” with words that start with a vowel sound
3.1. Example 1:an eagle
3.2. Example 2:It's a cat
3.3. Example 3:There is a shoe, and at the same time an image
