A vs. An
The article A is used before singular, countable nouns which begin with consonant sounds.
He is a teacher. She doesn't own a car. I saw a bear at the zoo
The article AN is used before singular, countable nouns which begin with vowel sounds.
He is an actor. She didn't get an invitation. I saw an eagle at the zoo.
If there is an adjective or an adverb-adjective combination before the noun, A(AN) should agree with the first sound in the adjective or the adverb-adjective combination.
He is an excellent teacher. I saw a really beautiful eagle at the zoo.
Use AN before words such as "hour" which sound like they start with a vowel even if the first letter is a consonant. Also use AN before letters and numbers which sound like they begin with a vowel, such as "F" or "8". Remember, it is the sound, not the spelling which is important. For example, "F" is pronounced "eff" like it starts with an "E".
I only have an hour for lunch. Sounds like "au-er". Does his name begin with an "F"? Sounds like "eff".
Remember that A(AN) means "one" or "a single". You cannot use A(AN) with plural nouns.
I saw a bears in Yellowstone National Park. Not Correct I saw bears in Yellowstone National Park. Correct
In English, some nouns are considered uncountable such as: information, air, advice, salt and fun. We do not use A(AN) with these uncountable nouns.
She gives a good advice. Not Correct She gives good advice. Correct
Use A before words such as "European" or "university" which sound like they start with a consonant even if the first letter is a vowel. Also use A before letters and numbers which sound like they begin with a consonant, such as "U", "J", "1" or "9". Remember, it is the sound, not the spelling which is important. For example, "1" is spelt O-N-E; however, it is pronounced "won" like it starts with a "W".
She has a euro. Sounds like "yu-ro". That number is a "1". Sounds like "won".