ADJECTIVES

An adjective is a word that tells us more about a noun. (By "noun" we include pronouns and noun phrases.)
An adjective "qualifies" or "modifies" a noun (a big dog).
Adjectives can be used before a noun (I like Chinese food) or after certain verbs (It is hard).

We can often use two or more adjectives together (a beautiful young French lady).

Determiners
the, a/an, this, some, any

Adjective Order
beautiful, long, dark brown

Comparative Adjectives
richer, more exciting

Superlative Adjectives
the richest, the most exciting

Gradable and Non-gradable Adjectives

see also:

Noun as Adjective
coffee cup, bus station, research centre

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It is sometimes said that the adjective is the enemy of the noun. This is because, very often, if we use the precise noun we don't need an adjective. For example, instead of saying "a large, impressive house" (2 adjectives + 1 noun) we could simply say "a mansion" (1 noun).