An adjective is a word that describes a noun:
The black cat climbed a tree.
The man felt a paralyzing fear.
Cinnamon-flavored oatmeal tastes better than plain.
The usual place of the adjective in an English sentence is in front of the noun it describes.
Sometimes, for poetic or literary effect, an adjective may occur after the noun it describes, as in the book title, Sarah, Plain and Tall.
A poem by Edgar Allan Poe begins, “Once upon a midnight dreary…” The adjective dreary follows the word it describes, midnight.
In a sentence that contains a being verb, an adjective used to complete the sentence will follow the verb.
Those dogs are friendly.
Prince George is young.
The kitten seems nervous.
You can have a whole string of adjectives if you wish:
The tall, thin, evil-looking cowboy roped the short, fat, inoffensive calf.
NOTE: The word the is a special kind of adjective called a definite article. It does not describe a noun, but points one out. The words a and an are forms of the indefinite article.