Do you know what an article is in English grammar?

1. More examples here:

1.1. I’m Mario. I’m a reporter

1.2. I´m Katy. I´m a Teacher

1.3. I´m Robert. I´m an actor

1.4. I´m Diane. I´m an artist

2. 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.

2.1. Examples

2.1.1. "a" I´m a student "an"

3. In the example given above, you can observe the word that follows the article “a”, and as you can see it is a word that starts with a consonant sound, so basically this articles which are called indefinite articles because implies that the thing referred to is nonspecific; follow the following uses:

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

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