Here are the plural forms of the singular nouns and articles, as well as the singular forms of the plural nouns and articles:
Singular Noun: Plural Noun
1. Le livre (the book) --> Les livres (the books)
2. L'oiseau (the bird) --> Les oiseaux (the birds)
3. La chaise (the chair) --> Les chaises (the chairs)
4. L'ami (the friend) --> Les amis (the friends)
5. Le stylo (the pen) --> Les stylos (the pens)
6. La table (the table) --> Les tables (the tables)
Singular Article: Plural Article
7. Un livre (a book) --> Des livres (some books)
8. Un oiseau (a bird) --> Des oiseaux (some birds)
9. Une chaise (a chair) --> Des chaises (some chairs)
10. Un ami (a friend) --> Des amis (some friends)
11. Un stylo (a pen) --> Des stylos (some pens)
12. Une table (a table) --> Des tables (some tables)
Remember that in French, the noun and article must agree in gender (masculine or feminine) and number (singular or plural).