why in this sentence it's using "a"?
shouldn't we use "an" for word who beginning with vowels?

Bir çeviriye bakın

"A" is used with words that begin with a consonant *sound*.
"An" is used with words that begin with a vowel *sound*.

For example:

a baby, a car, a dog, a hair, a hand, a hat, a hawk, a heatwave, a herb, a hill, a home, a horrible man, a hot pepper, a house, a human, a humble man, a one-off, a ‘u’ (= the letter ‘u’), a unicorn, a uniform, a unique opportunity, a unit, a university, a ‘y’ (= the letter ‘y’), a year, a yellow car

an apartment, an apple, an echo, an ‘h’ (= the letter ‘h’), an honest man, an honour, an honourable man, an hour, an item, an onion, an umbrella, an urn