The Indefinite Articles A and AN are part of basic English.
If you are a beginner, you will find this video helpful.
A or An – The Indefinite Articles
The difference of “a” and “an”
You can use “a” and “an” for all genders in the singular.
If you have to use “a” and “an”, depends on the sound the word begins with.
If the first sound is a consonant you have to use a.
If the first sound is a vowel you have to use an.
an ice cream
an hour – because the first letter is silent and the word starts with an au-sound.
a uniform, a university – because the first letter starts with a ju-sound.
Use of the indefinite article “a” and “an”
1. We can use a and an before countable nouns:
That’s a fast car. My aunt has got a big house.
2. We often use a and an to tell what someone/something is and what someone/something is like in the singular:
A hamster is an animal. Sarah is a very smart girl. Her dad is a mechanic.
Shakespeare is an English writer. Lisa has got a small nose.
3. We use “a” and “an” if the listener doesn’t know which thing we mean:
Frank sat down on a sofa. (we don’t know which sofa)
Do you have a bike? (it’s not a particular bike)
4. We use a and an before phrases of time and measurements:
We can do these exercises in an hour. The mangos are $3.50 a kilo.
Our neighbours go on holidays three times a year.