Ho letto il libro intero.

Ho letto is the passato prossimo, a very common Italian past tense used to talk about completed actions.

• ho = I have
• letto = past participle of leggere (to read)

So grammatically, it is like I have read, although in English we often translate it more naturally as I read depending on context.

In this sentence, it tells you that the action of reading the book was completed.

In Italian, the passato prossimo is formed with either avere or essere plus a past participle.

Leggere takes avere, so you say:

• ho letto
• hai letto
• ha letto

not sono letto.

A very useful rule is:

• most transitive verbs (verbs that take a direct object, like read a book) use avere
• many verbs of movement/change of state and reflexive verbs use essere

Since leggere can take a direct object like il libro, it uses avere.

Italian often leaves out subject pronouns when they are clear from the verb form.

• Ho letto already tells you the subject is I
• so io is not necessary

You could say Io ho letto il libro intero, but that usually adds emphasis, contrast, or clarification:

• Io ho letto il libro intero, lui no.
  I read the whole book, he didn’t.

So the version without io is the most neutral and natural one.

Il is the masculine singular definite article, meaning the.

So:

• il libro = the book

Italian uses articles more regularly than English does. Here, the speaker is referring to a specific book, so il is natural.

Also:

• libro is masculine singular
• therefore the article must also be masculine singular: il

Intero means whole or entire.

In il libro intero, it modifies libro, so the phrase means:

• the whole book
• the entire book

It emphasizes that the speaker read all of it, not just part of it.

Both are possible in Italian, but they do not feel exactly the same.

• il libro intero is very natural and common for the whole book
• l’intero libro is also correct, but it can sound slightly more formal, literary, or emphatic

In everyday speech, Italians very often use the adjective after the noun, as in:

• Ho letto il libro intero.

So this word order is normal and idiomatic.

Because it agrees with libro, which is masculine singular.

Italian adjectives usually agree in gender and number with the noun they describe.

Here:

• libro = masculine singular
• so intero = masculine singular

Compare:

• il libro intero = the whole book
• la pagina intera = the whole page
• i libri interi = the whole books
• le pagine intere = the whole pages

Because in this sentence letto is part of the verb, not an adjective.

In ho letto, letto is the past participle of leggere. With avere, the past participle usually does not agree with the direct object.

So you say:

• Ho letto il libro
• Ho letto la rivista
• Ho letto i giornali

The participle stays letto.

A more advanced note: agreement can happen in some cases when a direct object pronoun comes before the verb, but that is not what is happening here.

Yes. Ho letto tutto il libro is very common and often means almost the same thing.

Compare:

• Ho letto il libro intero
• Ho letto tutto il libro

Both mean I read the whole book.

A small nuance:

• tutto il libro is extremely common in everyday Italian
• il libro intero can sound a bit more emphatic, as if stressing completeness

Both are correct and natural.

Yes, Italian word order is somewhat flexible, although some versions sound more natural than others.

The most neutral version here is:

• Ho letto il libro intero.

You may also hear:

• Il libro intero l’ho letto.
  This gives emphasis to the whole book.

• Ho letto intero il libro.
  This is possible, but less natural in ordinary speech.

So the original sentence is a very standard and natural choice.

It normally describes a completed action in the past.

Passato prossimo is typically used for something that happened and was completed:

• Ho letto il libro intero. = I finished reading the whole book.

If you wanted to talk about a habitual action in the past, Italian would often use the imperfetto instead, though with this specific sentence the idea of the whole book naturally points to completion.

The h in ho is silent.

So ho is pronounced like o.

The h is there to distinguish forms of the verb avere in writing:

• ho = I have
• hai = you have
• ha = he/she has
• hanno = they have

Without the h, some of these would be confused with other words:

• o = or
• ai = to the
• a = to
• anno = year

So the h matters in spelling, but not in pronunciation.