Your young English teacher

[Gamerguy92]

Everytime you have a vowel (a, e, i, o, u, y) at the beginning of a word, you use 'an'.
For example:
An apple
An elephant
An Iguana
An omelette
An uzo
An year
There are few exeptions too:
An hour

Very well explained.
The letter Y is usually considered as a consonant in modern English.
The language has the exceptions and confusion because several letters have been dropped over the centuries, Yogh, Thorn, Wynn, Ash, were all replaced during the printing revolution with the standard letters today.