In English grammar, an adjective is any word that modify nouns and pronouns, primarily by describing a particular quality of the word they are modifying.
Adjectives are regularly located before the words they describe.

They provide full information about the noun. They may have origin words that end with -able, -ous, -er, est and -al. 
Adjectives frequently answer three questions about the nouns they describe: how many?/ 
what kind?/ which one?

Adjectives describe nouns by answering one of these three questions:

To describe:What kind is it?
To quantify: How many are there?
To identify: Which one is it?

Adjectives can be a single word, a phrase, or a clause.

EXAMPLES:

What kind is it?
A man with a cold greedy heart will never ask a lady to share his life and money. 
What kind of man? heartless and greedy.

How many are there?
The troublesome class, which have seventeen lazy under graded students from boys and 
five absent-minded aggressive girls, pretended that a UFO broke the windows.
How many students? twenty-two.

Which one is it?
The most unbelievable people in the planet are the snob fake friends, who abandon you 
when you’re in need.
Which ones? snob fake friends.