Words that introduce a noun are called determiners. There are various types which perform various tasks, including articles, quantifiers, demonstratives and possessives.
Definite article: the
Indefinite articles: a, an. “A” is used before a consonant; “an” is used before a vowel.
“The ducks flew away.”
“If I had a hammer, I probably wouldn’t hammer in the morning.”
“An apple a day keeps the doctor away.”
“An ounce of prevention is worth a pound of cure.”
These words show the quantity of a noun, either countable or non-countable. There is quite a list of quantifiers, including words such as some, little, few, much and each.
“I have seen few cowboys in my time in Colorado.” (count)
“In the desert, there are many camels.” (count)
“Much snow has fallen in a short time.” (non-count)
There are four demonstrative determiners: that, this, those and these. These words can also serve as demonstrative pronouns. In a sentence, the nouns that these words point to follow after.
“That purse is mine.”
“This is your cheeseburger.”
“Please exit through those doors.”
“Take these clothes to your room.”
Possessive determiners indicate the ownership of the noun that follows. The possessive adjectives are our, my, his, its, their, her and your. They differ from possessive pronouns in that the pronouns do not need to precede a noun and can stand alone.
“Have you seen my car?”
“The banana pudding in your fridge was delicious.”
“The cow is chewing its cud.”