Gramática-Repaso: Direct Object Pronouns, Realidades II, p 138
1. A direct object pronoun tells who or what receives the action of the verb
To avoid repeating a direct object noun, you can replace it with a direct objet pronoun. In English, him, her, and it, are examples of direct object pronouns. You have already used the following direct object pronouns in Spanish
singular
lo
la
plural
los
las
2. Diret object pronouns have the same gender (masculine or femenine) and number (singular or plural) as the nouns they replace. They come right before the conjugated verb.
¿Devolviste los libros a la biblioteca? No, no los devolví
¿Ayudaste a tu mamá en casa? Si, la ayudé
3. When an infinitve follows a verb, the direct object pronoun can be placed before the conjugated verb or attached to the infinitive
¿Sacaste el libro sobre Simón Bolivar? No, no lo pude sacar / No pude sacarlo