Adjectives are useful to describe nouns. With many adjectives, you can add -er or -est, e.g. 'a low wall', a 'lower wall', 'the lowest wall'. Others use more or most e.g. 'Bill is interesting', 'Bob is more interesting', 'Ben is the most interesting'.

Adjectives are 'describing words'. In the phrase 'the red balloon' the word 'red' is an adjective and the word 'balloon' is a noun. It is often the case that adjectives describe nouns.