Adjectives are words that are used to describe (what kind of?) nouns and pronouns and to quantify (how much of?) and identify (which one?) them. In a nutshell, Adjectives are what define nouns and give them characteristics to differentiate them from other nouns. For example:

He was wearing a blue  shirt.

Here ‘blue’ is an adjective as it is describing the noun ‘shirt’ by answering the question ‘what kind of shirt?’.