An indirect object is usually a person receiving the direct object. The indirect object pronouns in Spanish are basically the same as the ones used for the direct object, with the exception of those for the third person.It is important to remember that in Spanish, anytime that an indirect object is expressed, the pronoun must be present even if the indirect object is expressed in some other way (i.e., prepositional clause).
singular
plural
átono
tono
átono
tono
me
mí
nos
nosotros
te
ti
os
vosotros
le/se
él, ella, usted
les/se
ellos, ellas, ustedes
As you see, there is a pronoun that can be used only for the singular (le), other used only for the plural (les), and yet another one (se) that can be used for both, singular and plural. Nevertheless, the 'se' form is used only when the direct object pronoun is also used for reasons that seem to be primarily aesthetic (such as the use of the 'n' with the indefinite article in English: "an apple" vs. "a apple"). Although you'll see the pesky 'se' everywhere in standard writing in Spanish (i.e., newspaper articles, literature, manuals, etc.), you should be aware that there are many uses of 'se', and that it's not always used as an indirect object pronoun. First, let's see a few examples where we substitute the indirect object without using the direct object pronoun, and then we'll see how these two pronouns act together.
With prepositional clause
Le das el libro a Pedro.
You give the book to Pedro.
No prepositional clause
Le das el libro.
You give him the book.
With prepositional clause
Te doy el libro a ti. (redundant/emphasis)
I give the book to you
No prepositional clause
Te doy el libro.
I give you the book.
Note how in both languages we can use the prepositional clause to know who is receiving the book. The prepositional clause is mainly used for clarification or for emphasis. Generally in Spanish the prepositional clause is used at the end, whereas in English it would be incorrect to use it sometimes, as in the second sentence. In that case, we can identify the indirect object by using the name: "You give Pedro the book."
