How does the word sound?
"An" is used instead of "a" when the following word starts with a vowel sound. Vowel sounds are the sounds of the letters a, e, i, o, u.
A modification of the meaning of the next word and indicates one (any) person, thing, etc but not a particular one. Created to expand on meaning of words and can modify a large number of words.
Examples of how the word is used
|So, you want to buy a cat?|
|We will send the gift in a box!|