Naručiću novu knjigu sutra.

Because this is a common way to form the future tense in Serbian.

The full future form is built with:

• the auxiliary ću = I will
• the infinitive verb naručiti = to order

You can say:

• Ja ću naručiti novu knjigu sutra.
• Naručiću novu knjigu sutra.

When ću comes after the infinitive, Serbian usually writes it as one word and drops the final -ti of the infinitive:

• naručiti + ću → naručiću

So naručiću simply means I will order.

It is in the future tense, more specifically Future I in Serbian.

The key part is naručiću, which means I will order.

So the sentence is talking about a future action that will happen tomorrow.

Yes, it still clearly means I will order.

In Serbian, subject pronouns like ja (I) are often left out because the verb ending already shows who the subject is.

In naručiću, the ending tells you it is first person singular:

• I will order

You could add ja for emphasis:

• Ja ću naručiti novu knjigu sutra.

But in a neutral sentence, leaving it out is completely natural.

Because novu knjigu is in the accusative case, which is used here for the direct object of the verb.

The basic dictionary form is:

• nova knjiga = a new book

But after a verb like naručiti (to order), the object changes into the accusative:

• novu knjigu

Both words change because they are feminine singular:

• nova → novu
• knjiga → knjigu

So:

• nova knjiga = subject form
• novu knjigu = object form

Here naručiti means to order in the sense of:

• ordering a book
• ordering food
• placing an order for something

In this sentence, because the object is book, the meaning is clearly to order/purchase/request delivery of a book, not to command.

Sutra here is an adverb, meaning tomorrow.

It does not change for case in this use.

So in the sentence:

• Naručiću novu knjigu sutra.

  sutra simply tells you when the action will happen.

Yes. Serbian word order is fairly flexible.

This sentence can be rearranged in several natural ways, depending on emphasis:

• Naručiću novu knjigu sutra.
• Sutra ću naručiti novu knjigu.
• Novu knjigu ću naručiti sutra.

These all mean basically the same thing, but the emphasis shifts a little:

• sutra first emphasizes when
• novu knjigu first emphasizes what

The version you were given is a normal, natural sentence.

Yes, absolutely.

That is another correct way to say it.

Compare:

• Ja ću naručiti novu knjigu sutra.
• Naručiću novu knjigu sutra.

Both are correct. The difference is mostly style and emphasis:

• Ja ću naručiti... can sound slightly more explicit or contrastive
• Naručiću... is a compact, very common future form

Because naručiti is the perfective verb, and Serbian often uses a perfective verb in the future to describe a single completed action.

Here the idea is:

• tomorrow, I will place the order

That is one complete action, so naručiti fits well.

By contrast, naručivati is imperfective and would suggest repeated, ongoing, or habitual ordering in the right context.

So:

• naručiću = I will order / I will place the order
• naručivaću = I will be ordering / I will order repeatedly

Ću is pronounced with ć, a soft sound somewhat like a very soft ch.

A rough guide:

• ću sounds approximately like tyoo or a soft chyoo, though neither English spelling is exact

So naručiću is roughly:

• na-roo-CHEE-tyoo, with the last part softer than normal English ch

The important thing is that ć is softer than č.

By itself, novu knjigu most naturally means a new book.

Serbian does not have articles like a and the, so context decides whether something is definite or indefinite.

So depending on the situation, it could mean:

• I will order a new book tomorrow
• I will order the new book tomorrow

But without extra context, English learners usually translate it as a new book.