Moj brat će nam doneti tortu.

Because moj has to agree with brat in gender, number, and case.

Here, brat is:

• masculine
• singular
• nominative (because it is the subject)

So the correct form is moj brat.

If the noun changed, moj would change too. For example:

• moja sestra = my sister
• mog brata = of my brother / my brother (in some other cases)
• mom bratu = to my brother

Brat is in the nominative case.

It is the subject of the sentence, the person doing the action:

• Moj brat = the one who will bring the cake

In Serbian, the subject is usually in the nominative.

Će is the future-tense auxiliary.

More specifically, it is the 3rd person singular clitic form used to make the future:

• ja ću
• ti ćeš
• on/ona/ono će
• mi ćemo
• vi ćete
• oni/one/ona će

So in Moj brat će nam doneti tortu, će means will.

Because će is a clitic, and clitics in Serbian normally go in second position in the sentence or clause.

So:

• Moj brat će nam doneti tortu. is natural.
• Će moj brat nam doneti tortu. is not normal standard word order.

The first element is Moj brat, and then the clitic će comes right after that unit.

This sentence uses the common Serbian future pattern:

• clitic form of hteti
  • infinitive

So:

• će = will
• doneti = to bring

Together:

• će doneti = will bring

A very close alternative is:

• Moj brat doneće nam tortu.

That version is also future tense, but formed slightly differently in surface structure.

Nam is the dative plural clitic of mi.

It means:

• to us
• sometimes for us, depending on context

So here:

• Moj brat će nam doneti tortu = My brother will bring us a cake / will bring a cake to us

Why not the others?

• mi = we
• nas = us (usually accusative or genitive)
• nam = to us (dative)

Because the cake is being brought to someone, the dative is used.

Because tortu is the accusative singular form of torta.

Here, torta is the direct object of the verb doneti:

• What will he bring? tortu

For many feminine nouns ending in -a, the accusative singular ends in -u:

• knjiga → knjigu
• sestra → sestru
• torta → tortu

So:

• torta = nominative
• tortu = accusative

This is about aspect, which is very important in Serbian.

• doneti = perfective
  It refers to a single completed action
• donositi = imperfective
  It refers to an action in progress, repeated action, or general/habitual bringing

In this sentence, the idea is that the brother will bring the cake as one completed future event, so doneti is the natural choice.

Compare:

• Moj brat će nam doneti tortu. = He will bring us a cake.
• Moj brat će nam donositi tortu. = He will be bringing us cake / he will bring us cake repeatedly

Yes, Serbian word order is fairly flexible, but clitics like će and nam still follow special placement rules.

Possible variations include:

• Moj brat će nam doneti tortu.
• Tortu će nam doneti moj brat.
• Doneće nam tortu moj brat.

These all mean roughly the same thing, but the focus changes.

For example:

• Tortu će nam doneti moj brat. emphasizes the cake
• Moj brat će nam doneti tortu. is more neutral

What usually does not change freely is the internal order of the clitics:

• će nam is normal
• nam će is not normal here

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

So tortu can mean:

• a cake
• the cake

Which one is meant depends on the context.

That is very normal in Serbian. Learners often want to add an article, but Serbian simply does not use one.

Yes. That depends on the pronunciation standard or regional variety.

Two common variants are:

• doneti = Ekavian
• donijeti = Ijekavian

So you may see:

• Moj brat će nam doneti tortu.
• Moj brat će nam donijeti tortu.

Both are correct in their own standard varieties. The grammar is the same; the difference is mainly in pronunciation and spelling tradition.

The meaning is basically the same:

• Moj brat će nam doneti tortu.
• Moj brat doneće nam tortu.

Both mean My brother will bring us a cake.

The difference is in how the future form is built on the surface:

• će doneti = auxiliary + infinitive
• doneće = fused future form

In modern Serbian, both can be found, though the separate form će doneti is extremely common and very clear for learners.

The letter ć is a soft consonant that does not exist exactly in English.

So će is pronounced approximately like:

• a very soft cheh
• or tyeh, depending on how you hear it

It is not the same as č:

• č is harder, more like English ch
• ć is softer

So će should sound softer than English che.