Het boek heeft tachtig pagina's.

Because boek is a het-word in Dutch. Dutch nouns with the take either de or het, and you usually have to learn which article belongs with each noun.

• het boek = the book
• plural: de boeken = the books

A useful thing to remember is that all plural nouns take de, even if the singular uses het.

Heeft is the third-person singular present tense form of hebben (to have).

The verb forms are:

• ik heb = I have
• jij hebt / heb jij = you have
• hij/zij/het heeft = he/she/it has
• wij hebben = we have
• jullie hebben = you all have
• zij hebben = they have

Since het boek is singular and works like it, Dutch uses heeft.

Dutch normally uses hebben here, just like English: a book has pages.

So:

• Het boek heeft tachtig pagina's. = The book has eighty pages.

Using zijn here would sound wrong in standard Dutch.

Another very common alternative is:

• Het boek telt tachtig pagina's. = The book counts/contains eighty pages.

That is also natural Dutch.

This is normal Dutch main-clause word order: the finite verb goes in the second position.

So the pattern here is:

• Het boek = subject
• heeft = finite verb
• tachtig pagina's = rest of the sentence

Because the subject comes first, the verb comes right after it.

If you start with something else, the verb still stays in second position:

• Vandaag heeft het boek tachtig pagina's.

That verb-second rule is one of the most important things in Dutch word order.

Dutch numbers usually do not change form before nouns.

So you say:

• tachtig pagina's
• drie boeken
• vijf dagen

Unlike adjectives, numbers do not get extra endings here.

The apostrophe is there because the singular noun ends in a vowel: pagina.

In Dutch, many nouns ending in a vowel form the plural with 's instead of just s, mainly to make the spelling and pronunciation clear.

So:

• pagina → pagina's
• auto → auto's
• menu → menu's
• baby → baby's

Without the apostrophe, paginas would look odd in Dutch spelling.

No. Most Dutch plurals do not use an apostrophe.

Very common plural endings are:

• -en: boek → boeken
• -s: tafel → tafels

The apostrophe is mainly used in certain spelling situations, especially with words ending in a vowel, like:

• foto's
• oma's
• taxi's

So pagina's is a spelling rule, not the general way Dutch makes plurals.

Yes, both can mean pages, but they are not always used in exactly the same way.

• pagina often refers to a page as a numbered page, especially in books, magazines, websites, and documents.
• bladzijde can also mean page, often with a slightly more traditional or physical page of a book feel.

In this sentence, pagina's sounds completely natural.

You could also say:

• Het boek heeft tachtig bladzijden.

That is also correct.

A rough pronunciation is TAKH-tikh.

The tricky part is the Dutch ch/g sound, which is not like English ch in church. It is a throat sound.

A simple breakdown:

• tach: the a is short, and ch is that harsh Dutch sound
• tig: the last part sounds a bit like tikh, again with that Dutch guttural sound at the end in many accents

If saying the guttural sound is difficult at first, that is very normal for English speakers.

Because the subject is the book, and that is just one book.

The thing that is plural is pagina's (pages), not boek.

So the grammar is:

• Het boek = singular subject
• heeft = singular verb form
• tachtig pagina's = plural object/complement

English works the same way:

• The book has eighty pages.

Not:

• The book have eighty pages.

Yes, if you mean a book rather than the book.

• Het boek heeft tachtig pagina's. = The book has eighty pages.
• Een boek heeft tachtig pagina's. = A book has eighty pages.

So the difference is just definite versus indefinite:

• het = the
• een = a/an

Both are grammatically correct; they just mean different things.