Why is it 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.
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.
Is it an or a before user? So we see that it starts with [j] which is generally considered to be a consonant sound. Therefore we should say and write a user and not “an user” since we use “a” before a word which begins with a consonantal sound.
Why do you say a user? It’s a because the first sound of user is not a vowel, but the consonant /j/. ‘Vowel’ and ‘consonant’ describe letters that represent vowel and consonant sounds, but they also describe the sounds themselves. A vowel is a sound made from the throat without interruption by the other vocal organs.