El libro tiene cien páginas.

Because tener is the infinitive, meaning to have. In a normal sentence, the verb has to be conjugated to match the subject.

Here, the subject is el libro, which is third-person singular, so the correct form is tiene.

Present-tense forms of tener:

• yo tengo = I have
• tú tienes = you have
• él/ella/usted tiene = he/she/you have
• nosotros tenemos = we have
• ustedes tienen = you all have
• ellos/ellas tienen = they have

Because Spanish uses tener to talk about possession or what something contains or includes.

So a book can have pages:

• El libro tiene cien páginas.

This is more natural than using ser or estar, and different from hay.

Compare:

• El libro tiene cien páginas. = The book has one hundred pages.
• Hay cien páginas en el libro. = There are one hundred pages in the book.

Both can make sense, but tener is the most natural choice when the book is the thing being described.

In Spanish, it is very common to use an article like el or la where English might or might not use the.

Here, el libro means the book. It sounds like you are talking about a specific book.

If you say only libro, that usually would not work as a complete subject in a normal sentence like this.

Because libro is a masculine noun in Spanish, so it takes the masculine singular article el.

• el libro = the book
• la página = the page

This is grammatical gender, not biological gender. Objects can be masculine or feminine in Spanish, and the article has to match the noun.

Because the sentence says there are one hundred pages, so the noun must be plural.

• una página = one page
• cien páginas = one hundred pages

Spanish works like English here: if the number is more than one, the noun is normally plural.

The accent mark shows where the stress goes.

Páginas is stressed on the first syllable: PÁ-gi-nas.

Without the accent mark, standard Spanish stress rules would make you stress the second-to-last syllable instead, which would sound different.

So the accent is there to show the correct pronunciation.

Spanish uses cien before a noun and for the exact number 100.

So:

• cien páginas = one hundred pages
• cien = 100

But ciento is used when the number continues:

• ciento uno = 101
• ciento veinte = 120

So ciento páginas is incorrect.

No. Cien does not change for gender.

So you say:

• cien páginas
• cien libros

It stays cien with both masculine and feminine nouns.

Some other hundreds do change:

• doscientos libros
• doscientas páginas

But cien itself does not.

In Latin American Spanish, cien is usually pronounced roughly like syen in one syllable.

A quick guide:

• El ≈ ell
• libro ≈ LEE-bro
• tiene ≈ TYEH-ne
• cien ≈ syen
• páginas ≈ PAH-hee-nas

A couple of notes:

• The c in cien sounds like s in Latin America.
• The g in páginas sounds like a strong h sound before i.

The endings -o and -a are very common gender patterns:

• nouns ending in -o are often masculine
• nouns ending in -a are often feminine

So:

• libro → masculine
• página → feminine

But this is not a perfect rule. There are exceptions in Spanish, so it is best to learn each noun together with its article:

• el libro
• la página

That helps you remember the gender naturally.

Yes. In many contexts, you can write:

• El libro tiene 100 páginas.

That is perfectly normal.

Writing cien instead of 100 is also correct. Which one is preferred can depend on style, formality, and whether you are writing a sentence, a label, or something technical.

Yes, but El libro tiene cien páginas is the most neutral and standard order.

Spanish usually prefers:

• subject + verb + object

So:

• El libro = subject
• tiene = verb
• cien páginas = object

You might sometimes hear a different order for emphasis, but for learners, this sentence is the best model to follow.

It would be:

• El libro tiene una página.

Notice two things:

• una is feminine singular because página is feminine
• página becomes singular because there is only one page

So the number and the noun have to match:

• una página
• cien páginas