Ja danas kupujem poklon i cveće za nju.

Yes. In Serbian, the verb ending already shows the subject, so kupujem by itself means I am buying / I buy.

That means ja is often optional. It is included here for one of these reasons:

• to make the subject explicit
• to add emphasis
• to create contrast, like I’m buying it, not someone else

So both are possible:

• Ja danas kupujem poklon i cveće za nju.
• Danas kupujem poklon i cveće za nju.

The version with ja sounds a bit more explicit or emphatic.

It can mean either, depending on context.

The Serbian present tense often covers both:

• I buy
• I am buying

In this sentence, because of danas (today), English will usually prefer I am buying or sometimes I’m buying ... today.

So kupujem is present tense, but English may translate it in different ways depending on the situation.

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

• kupovati / kupujem = imperfective
• kupiti / kupim = perfective

Here, kupujem is used because the action is viewed as ongoing, current, planned, or simply happening in the present.

A very important point: the present tense of a perfective verb like kupim usually does not mean a normal present action. It usually refers to a future completed action.

So:

• Danas kupujem... = Today I’m buying...
• Danas kupim... would not normally be used this way

For a straightforward present-day action, kupujem is the natural choice.

It is in the object case: accusative.

But for a masculine inanimate singular noun, the accusative is often the same as the nominative.

So:

• nominative: poklon
• accusative: poklon

That is why it looks unchanged.

If it were a masculine animate noun, you would often see a different form in the accusative. But poklon is inanimate, so nominative and accusative match.

Cveće is a very common Serbian word meaning flowers in a collective or mass sense.

It works a bit like a singular mass noun grammatically, even though in English we usually translate it as plural flowers.

So in Serbian:

• cveće is grammatically neuter singular
• but in meaning, it often refers to flowers in general or a bunch of flowers

That is why poklon i cveće is a very natural pairing: a gift and flowers.

You may also meet words based on cvet (flower), but cveće is the normal everyday word in this kind of sentence.

There are two important things here.

First, the preposition za requires the accusative case.

The pronoun ona (she) changes like this:

• nominative: ona
• accusative: nju

So after za, you need nju:

• za nju = for her

Second, je is a clitic form and cannot be used after a preposition like za. After prepositions, Serbian uses the full stressed form, so nju is correct.

As for joj: that is the dative form, and you can use it in a different structure:

• Kupujem joj poklon i cveće. = I’m buying her a gift and flowers.

That is also natural Serbian. The version with za nju is more literally for her.

Yes, but the difference is small.

• Kupujem joj poklon i cveće.
  This is a very natural dative construction: I’m buying her a gift and flowers.

• Kupujem poklon i cveće za nju.
  This more explicitly says for her.

In many everyday situations, both work well. The version with za nju can sound slightly more explicit or contrastive, especially if you want to stress who the items are for.

For example:

• Ne za njega, nego za nju.
  Not for him, but for her.

No. Serbian word order is fairly flexible.

The sentence:

• Ja danas kupujem poklon i cveće za nju.

could also appear as:

• Danas kupujem poklon i cveće za nju.
• Poklon i cveće danas kupujem za nju.
• Za nju danas kupujem poklon i cveće.

These versions do not all sound equally neutral, though. The original order is very natural and straightforward.

In Serbian, moving words around often changes:

• emphasis
• focus
• what sounds new or important

So the word order is flexible, but not random.

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

So:

• poklon can mean a gift or the gift
• cveće can mean flowers or the flowers

The exact meaning comes from context.

In this sentence, English naturally says a gift and flowers, but Serbian does not need separate article words to express that.

Yes, danas can move.

Here it appears after ja:

• Ja danas kupujem...

That is a normal, neutral placement. But Serbian allows other positions too:

• Danas ja kupujem...
• Ja kupujem danas...
• Danas kupujem...

The choice depends on rhythm, emphasis, and what the speaker wants to highlight. In a basic learner sentence, the original placement is natural and easy to understand.