Yes, you need "a" there.
Your first sentence should end with "I will accept and appreciate any help". There should be no semicolon after 'Please".
Hello Dear Teacher,
I am a new student here, and my level of English needs more improvement, so I will accept and be appreciated any help.
My question is about articles, specifically grammatically correct use of article "a" in the sentence " I am a US citizen".
Do I have to use an article in this case in front of a vowel? What is the right way to say " I am a US citizen" or " I am US citizen".
1. I am a British/Canadian/Danish/French citizen.
2. I am an American/Estonian/Indian citizen.
3. I am a European/US citizen.
We need the indefinite article in these sentences,
We need 'a' before a consonant sound (1) and 'an' before a vowel sound (2). The first sound of the nationality in (3) is /j/, which counts as a consonant.
You don't need an article to simply say "I'm American" because it's an adjective. You need the article in the others because it refers to "citizen". You can also say "I'm an American" - citizen/national is implied. Note that that doesn't work with all nationalities.
I'm a Brit.
I'm a British.
Remember - if you don't use correct capitalisation, punctuation and spacing, anything you write will be incorrect.