In French there are feminine and masculine adjectives, just as there are feminine and masculine nouns.
An adjective must have the same grammatical gender as its object.

Formation of the feminine adjective form:

(Exception: if the adjective already ends in «e».)

💬 For Example:

joli (m) (pretty) → jolie (f) nouveau (m) (new) → nouvelle (f)

The plural formation of adjectives complies to the plural formation of substantives.

💬 For Example:

jolis (m, pl) → jolies (f, pl) nouveaux (m, pl) → nouvelles (f, pl)

Adjectives and their position within the sentence:

Commonly the adjective is to be found after the substantive.

💬 For Example:

La couleur bleue est très belle. - The colour blue is very beautiful.

The following adjectives are exceptions to this rule:

→ petit, grande, gros (small, big, thick):
💬 For Example:

une petite femme - she’s a small woman

→ vieux, jeune (old, young): un vieil arbre (an old tree)
→ mauvais, bon (bad, good)
→ long, court, bref (long, short, brief)
→ beau, joli, vilain (beautiful, pretty, ugly)