1. Noun / Adjective Agreement
In Spanish, all nouns have gender [masculine/feminine] and number [singular/plural].

2. Masculine Feminine
Chico chicos chica chicas
libro libros regla reglas
estudiante estudiantes

3. In Spanish, all adjectives must agree with the noun they describe in both gender and number. Every adjective has both a singular and plural form; and a masculine and feminine form. A descriptive adjective usually follows the noun it describes.

4. Most nouns that end in “o” are masculine
Most nouns that end in “o” are masculine. One noun that ends in “o”, but is feminine is :
la mano – the hand

5. Nouns that end in the following are normally feminine:
-a la muchacha the girl
-ción la nación the nation
-sión la misión the mission
-tad la libertad the liberty
-dad la nacionalidad the nationality

6. Hay un libro rojo aquí. There is a red book here.
Hay una regla roja aquí. There is a red ruler here.

7. Adjectives that show quantity [how much / how many] and question-asking words usually go before the noun they describe.

8. Tengo dos libros verdes. I have two green books.
¿Cuántas reglas hay? How many rulers are there?
¿Cuántos libros hay? How many books are there?

9. Hay dos libros rojos aquí. There are two red books here.
Hay dos reglas rojas aquí. There are two red rulers here.