Indefinite Articles:

“a” and “an” are called “indefinite articles”.

Uses of “A” and “AN”:

They are used to talk about things in general.
For example:

1. I saw “a dog” in the street.
   “a” dog refers to any dog.
2. I saw “an” Elephant in the zoo”.
   “an elephant” refers to any elephant in the zoo.

“a” is used:

1. Before singlular nouns if it is a “consonant”-a book, a car, a dog, a zoo, a rat.
2. Before singular nouns beginning with consonant sound-University, Uniform, User.
   Note: Though “U” is a vowel, sometimes, it has a consonant sound.
3. Before nouns starting with a pronounced “h” sound-horse, high.

An is used: <./h2> Before singular noun starting with a “vowel”. Before singular nouns starting with silent “H”.-hour, honest.
Note: Though “h” is a consonant, “an” is used when “h” is silent. Note:
In some words where “H” is pronounced, such as “Historical”, “an” is used.

Membership of a group:

The indefinite articles are used to indicate membership of a group:
Example:
I am a teacher.
He is an Irish.