1. A
1.1. In general the article "A" is in used when it is goes by a consonant.
1.1.1. Examples:
1.1.1.1. This is a book
1.1.1.2. You have a beatiful garden
1.1.1.3. Diana have a white cat
1.1.1.4. I have a pineapple
1.2. But there are certain rules and exceptions for his use:
1.2.1. Nouns that begin with "eu" - "ur"
1.2.1.1. Examples:
1.2.1.1.1. eu
1.2.1.1.2. ur
1.2.1.1.3. He is a urologist
1.2.1.1.4. This is a urban transport
1.2.2. Those who start with "U" and the beginnig are heard as "iu"
1.2.2.1. Examples:
1.2.2.1.1. A university
1.2.2.1.2. My draw is a unicorn
1.2.2.1.3. he isn´t a uninvited.
1.2.3. When the word begins with "H"ans this letter is heard as J in spanish.
1.2.3.1. Examples:
1.2.3.1.1. He have a hat
1.2.3.1.2. Is a hard day in the job
1.2.3.1.3. a huge heart
2. AN
2.1. In general the article "An" is in used when it is goes by a vocal.
2.1.1. Examples:
2.1.1.1. I have an apple.
2.1.1.2. It isn´t an easy question
2.1.1.3. It is an ugly hotel.
2.2. However, there also certain rules and exceptions that must be followed:
2.2.1. when it is a word with "H" silent, then we must use "AN"
2.2.1.1. Examples:
2.2.1.1.1. An hour.
2.2.1.1.2. An honourable man.
2.2.1.1.3. An honest mistake.
3. OTHER RULES:
3.1. We can't used A/AN with countiess nouns
3.1.1. Example:
3.1.1.1. A sugar
3.1.1.2. A milk
3.1.1.3. A water
3.2. We can't used A/AN with plural nouns
3.2.1. Examples:
3.2.1.1. A chairs
3.2.1.2. An ears.