1. S + V + who or what = direct object
The Direct Object is the person, place or thing that directly receives the action of the verb.
S + V + who or what = direct object
Paco – needs - a book.
Subject - Verb - Direct object

2. Paco is buying a book for Marta. Paco is buying it for Marta.
The Direct Object will only be represented once in a sentence, either with the noun or the pronoun - never both.
Paco is buying a book for Marta. Or
Paco is buying it for Marta.

3. Direct object pronouns
me nos Te
lo – it los - them
la - it las - them

4. If it is the object of conjugated verb - then place it before the verb.
Marcos come el pollo
Marcos lo come

5. If it is the object of a verb infinitive
then you can attach it to the end of the
infinitive or place it before the
conjugated verb.
ie…Marta quiere comerlo.
Or Marta lo quiere comer.

6. Ejemplos.. Paco has a book in his backpack.
Paco tiene un libro en su mochila.
Paco has it in his backpack.
Paco lo tiene en su mochila.
*If a direct object noun is used in English, then a direct object noun will be used in Spanish. If a pronoun, then a pronoun.

7. Where do you place the direct object pronoun if it is the object of the conjugated verb?
In front of the conjugated verb

8. Where do you place the direct object pronoun if it is the object an infinitive?
Either before the conjugated verb or attached to the end of the infinitive