You will see several different types of object pronouns:

1. ) direct objects
2. ) indirect objects,
3. ) objects of preposition,
4. ) reflexive pronouns,
5. ) the passive “si,” 
6. )and  ci and ne.

1) Direct objects

A direct object receives the action of the verb and answers the question, “What?” For example:

• Vedo la ragazza. I see the girl.

We can ask, “What do I see?” and answer “The girl.” So “la ragazza” is our direct object.

Just like how in English we can replace “the girl” with the pronoun “her,” in Italian we can replace direct objects with pronouns. The direct object pronouns are the following:

Usually these pronouns come before your verb. So the sentence “Vedo la ragazza” becomes “La vedo” (I see her).

Sometimes pronouns are put after the verb for emphasis, and then use a different set of pronouns, called tonic pronouns:

Except for “me” and “te,” these are the same forms as the subject pronouns. Going back to “Vedo la ragazza,” we can say “Vedo lei,” if we want to emphasize that it is her (not someone else).

2) Indirect objects

Like direct objects answer the question “What?” indirect objects usually answer the question “To whom?” or “For whom?” For example:

• Scrivo a mia sorella. I write to my sister.

“My sister” answers the question, “To whom do I write?” so “mia sorella” is the indirect object.

The indirect object pronouns look like the direct object pronouns, except the third person:

Like the direct object pronouns, these typically come before the verb:

• Scrivo a mia sorella. Le scrivo. I write to my sister. I write to her.

You can also use the tonic pronouns (see above) after the verb for emphasis or clarification, but with the indirect object, “a” is required:

• Scrivo a lei.

The only exception is “loro,” which does not require “a”:

• Scrivo ai miei amici. Gli scrivo. / Scrivo loro. I write to my friends. I write to them.

3) Objects of preposition

After a preposition (for example, “con,” “di,” “per”), you should use a tonic pronoun (see above):

• Non so niente di te. I don’t know anything about you.

4) Reflexive pronouns

In Italian, some verbs are reflexive, meaning that the person doing the action does it to him or herself. Examples of this would be “mettersi” (to put a piece of clothing on), “chiamarsi” (literally “to call oneself”), and “sentirsi” (to feel). In the dictionary, you may notice that the infinitive has “si” on the end to show the verb is reflexive.

Reflexive verbs have their own pronouns:

These pronouns match the verb (“mi” with the “io” form, “ti” with “tu,” etc.) and are usually placed before the verb:

• Mi metto la giacca. I put on my coat.

5) The passive “si” (si passivante)

We use the passive or impersonal “si” when we don't want to state who exactly did the action. This can be translated in different ways in English. For example:

• In Italia si mangia la pizza.

This could be translated as: In Italy, pizza is eaten, In Italy, you (in general) eat pizza, In Italy, one eats pizza, In Italy, they (in general) eat pizza, among other things. The important thing to remember is that this action is not being done by any specific person.

To form this, use “si” and a verb in the third person (the form for lui/lei or loro). If there is an object after the verb, the verb agrees with the object. So we say:

• Si mangia la pizza.

but

• Si mangiano le pizze.

If there is no object, the verb is singular:

• Si mangia.

For reflexive verbs, you add “ci” before “si”:

• Ci si alza presto. One gets up early.

6) Ci and ne

“Ci” and “ne” replace prepositional phrases. “Ci” replaces “in” or “a” and their object:

• Vai a Roma? No, non ci vado. Are you going to Rome? No, I’m not going there.

“Ne” replaces “di” and its object:

• Vuoi una di queste caramelle? Ne vuoi una? Do you want one of these candies? Do you want one of them?