Potvrda porudžbine i broj za praćenje su u poruci.

Because porudžbine is in the genitive singular.

The base noun is porudžbina = order.
But after potvrda (confirmation), Serbian usually uses the genitive to show confirmation of what?

• potvrda porudžbine = confirmation of the order

So:

• nominative: porudžbina
• genitive singular: porudžbine

This is a very common pattern in Serbian:

• broj telefona = phone number
• adresa firme = company address
• potvrda porudžbine = order confirmation

Because the subject is compound: there are two things being talked about:

• potvrda porudžbine = the order confirmation
• broj za praćenje = the tracking number

These two are joined by i (and), so the subject is plural:

• Potvrda porudžbine i broj za praćenje su...

That is why Serbian uses:

• je = is
• su = are

So this sentence literally works like:

• The order confirmation and the tracking number are in the message.

Poruci is locative singular of poruka (message).

After the preposition u when it means in / inside / within, Serbian usually uses the locative:

• u poruci = in the message
• u kući = in the house
• u školi = at school / in school

So:

• nominative: poruka
• locative: poruci

Here u poruci means in the message.

Because u can be used with different cases depending on meaning.

With location (where something is), u takes the locative:

• u poruci = in the message
• u gradu = in the city

With direction (where something is going), u takes the accusative:

• idem u grad = I’m going to the city
• stavljam to u poruku = I’m putting that into the message

In your sentence, the meaning is location, not motion, so it is:

• u poruci

Literally, it is something like number for tracking.

Breakdown:

• broj = number
• za = for
• praćenje = tracking

So:

• broj za praćenje = tracking number

This is a very common Serbian structure:

• karte za koncert = tickets for the concert
• čaša za vodu = glass for water
• broj za praćenje = number for tracking

English often turns this into a compound noun (tracking number), while Serbian often uses noun + za + verbal noun/noun.

Here praćenje is a verbal noun meaning tracking.

The verb is:

• pratiti = to follow / track

From that, Serbian forms:

• praćenje = tracking, monitoring, following

After za, Serbian often uses this kind of noun:

• oprema za kuvanje = equipment for cooking
• vreme za spavanje = time for sleeping
• broj za praćenje = number for tracking

So this is not a verb form in the sentence; it is a noun-like form.

Yes. Serbian word order is more flexible than English word order.

The neutral order here is:

• Potvrda porudžbine i broj za praćenje su u poruci.

But depending on emphasis, Serbian could also say things like:

• U poruci su potvrda porudžbine i broj za praćenje.

That version emphasizes where they are: In the message are the order confirmation and the tracking number.

So yes, the order can change, but the original sentence sounds natural and neutral.

Because Serbian does not have articles like English a/an/the.

English says:

• the order confirmation
• the tracking number
• the message

Serbian simply uses the nouns without articles:

• potvrda porudžbine
• broj za praćenje
• poruka / poruci

Whether something means a or the usually depends on context.

So in this sentence, even though Serbian has no separate word for the, the full meaning is understood from the situation.

No. Another very common word is narudžbina.

So you may also see:

• Potvrda narudžbine i broj za praćenje su u poruci.

Both are used and both mean order in the shopping / delivery sense.
Which one appears more often can depend on region, company style, or personal preference.

For a learner, it is useful to recognize both:

• porudžbina
• narudžbina

Yes. I means and and joins the two noun phrases:

• potvrda porudžbine
• broj za praćenje

So together they form one plural subject.

A small point for English speakers: Serbian i is pronounced like English ee in see, not like the English word eye.

In standard Serbian, that would normally be considered incorrect, because the subject is plural in meaning: confirmation and number.

So the standard form is:

• Potvrda porudžbine i broj za praćenje su u poruci.

You need su because there are two coordinated items.

It is neutral and very natural, especially in business, e-commerce, and delivery contexts.

It sounds like something you might see in:

• an email
• a delivery notification
• an online shop message
• customer support communication

It is not especially formal, but it is completely appropriate in professional communication.

The subject is:

• Potvrda porudžbine i broj za praćenje

The verb is:

• su

The location phrase is:

• u poruci

A useful clue is the case ending:

• poruci is locative after u, so it is clearly part of a prepositional phrase, not the subject.
• The coordinated nouns before su are in the basic citation form and function as the subject.

So the structure is:

• [Subject] + [verb] + [location]
• Potvrda porudžbine i broj za praćenje + su + u poruci