What is right a user or an user? ‘A user’ is the correct usage. The usage of ‘a’ or ‘an’ depends on the sound of the letter that comes after it. So if the word starts with the sound of a vowel then ‘an’ is used before it, and if it starts with the sound of a consonant then ‘a’ is used before it.
Why a user and not an user? The choice of a or an is made based on pronunciation, not spelling. The only reason the word an exists is because a followed by another vowel is awkward to pronounce. Since user is pronounced /ˈjuːzə/, starting with a consonant “y” sound, the article a is appropriate, and an is not.
When to user a or an? If the first letter makes a vowel-type sound, you use “an”; if the first letter would make a consonant-type sound, you use “a.” However, even if you follow these basic rules when deciding to use “a” or “an,” remember that there are some exceptions to these rules. “A” goes before words that begin with consonants.
Which is correct a used or an used? “A” is used before words starting in consonant sounds and “an” is used before words starting with vowel sounds. It doesn’t matter if the word is an adjective, a noun, an adverb, or anything else; the rule is exactly the same.