How does an adjective agree with the noun in French- 'accord de l'adjectif'?

General rule: The adjective agrees with the noun that it describes in gender and number:

Example:

1. La verte valet

2. Les vertes valets

3. Le pret vert

4. Les verts prets

So, if the noun is plural and female, the adjective will also be plural and female. 

Exception: Masculine adjectives ending with x or s do not change in the plural.

Un homme roux --> Des hommes roux