Le livre a onze pages.

Because livre is a masculine singular noun, so the correct definite article is le.

• le livre = the book
• un livre = a book

A native English speaker may expect noun gender to be obvious, but in French you simply have to learn it with the noun. Livre is masculine.

A is the third-person singular present form of avoir, which means to have.

So:

• Le livre a... = The book has...

Related forms:

• j'ai = I have
• tu as = you have
• il / elle a = he / she has

French normally uses avoir to talk about how many pages, years, or similar units something has.

So French says:

• Le livre a onze pages.
  Literally: The book has eleven pages.

That is the most natural way to express this idea in French. English can also say The book is eleven pages long, but French usually does not use that structure here.

After a cardinal number like deux, trois, onze, or cent, French normally puts the noun directly after the number, with no de.

Examples:

• deux pages
• onze pages
• cent pages

You often use de after expressions of quantity instead, such as:

• beaucoup de pages = a lot of pages
• peu de pages = few pages

So onze pages is correct.

Because onze means eleven, and anything more than one normally takes a plural noun in French.

So:

• une page = one page
• onze pages = eleven pages

The spelling changes by adding -s:

• page → pages

Usually, no. The final s in pages is normally silent.

So page and pages sound the same by themselves:

• page = /paʒ/
• pages = /paʒ/

The plural is shown in writing, but not usually heard in pronunciation unless there is a liaison in another context.

Onze is pronounced /ɔ̃z/.

A rough English-friendly approximation is onz, but the first sound is a nasal vowel, which English does not really have.

Important points:

• the final z is pronounced
• it does not sound like English once
• it begins with a vowel sound

Yes, it is very similar here.

The structure is:

• Le = the
• livre = book
• a = has
• onze pages = eleven pages

So the pattern is:

article + noun + verb + number + noun

That is close to English: The book has eleven pages.

A careful pronunciation is:

/lə livʁ a ɔ̃z paʒ/

A rough English-style guide would be:

luh leevr ah onz pahzh

A few notes:

• livre has the French r, not an English r
• onze ends with a pronounced z
• pages ends with a soft zh sound
• the final s in pages is silent
• there is no special consonant linking between a and onze, because a already ends in a vowel sound