Njen brat danas kupuje poklon za nju.

A word-by-word breakdown is:

• njen = her
• brat = brother
• danas = today
• kupuje = is buying / buys
• poklon = gift
• za = for
• nju = her

So the whole sentence means something like Her brother is buying a gift for her today.

Njen is the possessive pronoun meaning her. It shows that the brother belongs to or is related to her:

• brat = brother
• njen brat = her brother

Serbian often uses possessive words like moj (my), tvoj (your), njegov (his), njen (her) in the same way English uses my, your, his, her.

Because njen has to agree with the noun it describes.

The noun brat is:

• masculine
• singular
• nominative here

So the possessive pronoun also takes the matching form:

• njen brat = her brother
• njena sestra = her sister
• njeno dete = her child

This is normal adjective-type agreement in Serbian.

Because brat is the subject of the sentence, and subjects are normally in the nominative case.

Here, njen brat is the person doing the action of buying. So nominative is used:

• Njen brat kupuje... = Her brother is buying...

If brother had a different role in the sentence, the form could change. For example:

• Vidim njenog brata. = I see her brother.

There, brata is not the subject, so it changes case.

It is changing case, but in this sentence the accusative form happens to look the same as the nominative.

Poklon is a masculine inanimate noun. For masculine inanimate nouns, nominative and accusative singular are usually identical:

• nominative: poklon
• accusative: poklon

Since poklon is the direct object of kupuje, it is in the accusative case, even though the form does not visibly change.

Compare that with a masculine animate noun, where the accusative usually does look different:

• brat → accusative brata

Because the preposition za requires the accusative here.

So:

• nju = accusative form of ona / she
• za nju = for her

That is why the sentence has:

• poklon za nju = a gift for her

If you used njoj, that would be a different case, usually dative/locative:

• Daje joj poklon. = He gives her a gift.

So:

• za nju = for her
• joj / njoj = to her

English often uses for and to in ways that Serbian separates more clearly through case and prepositions.

They are different case forms of she/her.

• nju = accusative
• joj = dative
• njoj = a stressed/full form of dative/locative

In this sentence, the structure is za + accusative, so we need nju:

• za nju = for her

But if the verb takes an indirect object, you often get joj:

• Kupuje joj poklon. = He is buying her a gift.

That sentence is slightly different in structure from:

• Kupuje poklon za nju. = He is buying a gift for her.

In many situations, both can be natural, but the grammar is not the same.

Kupuje is present tense.

In Serbian, the present tense of an imperfective verb can mean:

• is buying right now / around now
• buys habitually or generally

So without extra context, kupuje can be translated in more than one way.

With danas (today), the most natural English translation is usually:

• Her brother is buying a gift for her today

The verb here is from kupovati or used as an imperfective present form meaning ongoing/current action.

Yes, Serbian word order is flexible, and danas can move.

The given sentence:

• Njen brat danas kupuje poklon za nju.

is perfectly natural and means Her brother is buying a gift for her today.

You could also say:

• Danas njen brat kupuje poklon za nju.
• Njen brat kupuje danas poklon za nju.

These versions are all grammatical, but the emphasis changes a little depending on what you want to highlight.

Serbian uses word order more freely than English, because case endings help show what each word is doing.

Often yes, as long as the case forms still make the roles clear.

For example, these are all possible:

• Njen brat danas kupuje poklon za nju.
• Danas njen brat kupuje poklon za nju.
• Poklon za nju njen brat danas kupuje.

The basic meaning stays close, but the focus changes.

English relies heavily on word order for meaning. Serbian relies more on case plus context, so word order is freer.

Still, not every order sounds equally natural in every situation. The original sentence is a neutral, natural choice.

Because Serbian has no articles.

English distinguishes:

• a gift
• the gift

Serbian usually does not mark that difference with a separate word. So poklon can mean:

• a gift
• the gift

depending on context.

The same goes for brat:

• brat can mean a brother, the brother, or just brother depending on the situation.

Context tells you which meaning is intended.

Yes, that is also a very natural Serbian sentence.

• Njen brat joj danas kupuje poklon.

This means roughly the same thing: Her brother is buying her a gift today.

The difference is grammatical:

• poklon za nju = a gift for her
• joj kupuje poklon = he is buying her a gift

Both are common. The version with joj uses an indirect object. The version with za nju uses a prepositional phrase.

Sometimes one may sound slightly more natural depending on context, but both are correct.

Yes. Serbian verbs have aspect, and that matters a lot.

Here, kupuje is an imperfective present form. Imperfective verbs are commonly used for:

• ongoing action
• repeated action
• action viewed from the inside, not as a completed whole

So kupuje fits well with meanings like:

• is buying
• buys

If you wanted a future completed action, Serbian would usually use a different form, for example with the perfective verb kupiti:

• Njen brat će kupiti poklon za nju. = Her brother will buy a gift for her.

For a learner, the key point is: Serbian present-tense forms are tied not only to tense, but also to aspect.