how to use A, An, and The?

Answer 1

you use the before a noun
you use an in front of a word that begins with a vowel
you use a before all the other words that don't begin with a vowel

Answer 2

The word "a" in an indirect object pronoun. You use before a noun that starts with a consonant if the word is not referring to specific one. You use "an" in the same way but with nouns that start with vowels.
Example: I want a book. I want an apple
"The" is a direct object pronoun and is used when speaking about a specific object.
Example: I want the book.

Answer 3

you use a before a word beginning with a consonant-a mouse
you use an before a word starting with a vowel-an orange
and you use the before nouns,when you want to refer to a certain object-the books