a + vowel sound

[rezaa]

why is it sometimes we use the indefinite article 'a' even though it precedes a vowel sound? and when do we do so?
thank you

[Mister Micawber]

.
To my knowledge, we always use 'an', and never 'a', before a vowel sound. Confusion arises for learners when the vowel sound is represented by an alphabetic consonant.
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[rezaa]

these are some examples
Juan Dahlmann is a Argentinian library secretary.
.... Consolidate Debts with a unemployed refinance loans
I know a web-site where there is a undressed model picture.
What is a easy and good glue to use to on Lego blocks ...
What is a easy job that pays great?
even in english books and newspapers i've come across many but unfotunately i don't remember any :)

[Buddhaheart]

Juan Dahlmann is aW anU Argentinian library secretary.
.... Consolidate Debts with a W an Uunemployed refinance loans
I know a web-site where there is aW an U undressed model picture.
What is a W an Ueasy and good glue to use to on Lego blocks ...
What is aW anU easy job that pays great?

even in english books and newspapers i've come across many but unfotunately i don't remember any :) ??!!

Examples:

A hotel as the ‘h’ is silent.
A university as ‘u’ is considered a glide represented by /ju/ (IPA phonetic symbol) where it begins with a consonant sound.

[Harry Smith]

In the word "hotel" h isn't silent. H is silent in the words: honest and hour.

[Mister Micawber]

Juan Dahlmann is a Argentinian library secretary.
.... Consolidate Debts with a unemployed refinance loans
I know a web-site where there is a undressed model picture.
What is a easy and good glue to use to on Lego blocks ...
What is a easy job that pays great?

These are all illiterate examples, rezaa-- I presume that you pulled them off Google?-- Google examples cannot be trusted indiscriminately.

And, no, the 'h' of 'hotel' is not silent-- but it begins an unstressed initial syllable, and many competent native speakers opt to preface such words with 'an', which is also acceptable:

a/an hotel reservation
a/an Havana cigar
a/an Hawaiian vacation
a/an hallucinatory experience

And then there are some trans-Atlantic dichotomies:

a/an humble pie
a/an herb salad
a/an homage to Santa Roselia.
.

[Buddhaheart]

My apology. Indeed the ‘h’ in ‘hotel’ is not silent. I meant to say since it’s not silent, in today’s usage, the article ‘a’ is appropriate.

An old grammar rule states if a word begins with an ‘h’ and not accented on the 1st syllable, ‘an’ is often used; as,

An hotel, an historical novel.

This is as Mr. Micawbar suggested.

[RonBee]

I'm not from the South, so I don't say a hour, but that usage is common here (North Carolina). If you happen someday to travel in these parts don't decide you learned your English lessons wrongly. It's a regionalism. (We also say y'all here, and that's not exactly standard English. )

~R