Pozajmica će početi danas.

The subject is pozajmica.

It is a feminine singular noun in the nominative case. In this sentence, it is the thing that will start.

This is the Serbian Future I tense.

It is formed with:

• the clitic auxiliary će
• the infinitive početi

So:

• će = the future marker, similar to will
• početi = to begin / to start

Together, će početi means will begin / will start.

Because početi is the perfective verb, and Serbian often uses a perfective verb when talking about a single completed event in the future.

• početi = to start, viewed as one whole event
• počinjati = to be starting / to start repeatedly / to start in an ongoing or habitual sense

Here the sentence refers to one specific beginning, so početi is the natural choice.

Because će is a clitic.

In Serbian, clitics usually go in the second position of the sentence or clause. That means they often come after the first stressed word or phrase.

So in:

• Pozajmica će početi danas.

the first main word is pozajmica, and the clitic će comes right after it.

This is very normal Serbian word order.

Yes, in some word orders it can.

If the infinitive comes before će, the future is usually written as one word, and the infinitive loses -ti:

• početi + će → počeće

So you can have:

• Pozajmica će početi danas.
• Počeće danas pozajmica.

Both are grammatical, but they do not sound equally neutral in all contexts. The original sentence is the more straightforward, neutral order.

Danas is an adverb, meaning today.

It is not a noun here, so you do not analyze it as being in a case the way you would with a noun or pronoun. It simply tells you when the action happens.

Yes. Serbian word order is fairly flexible.

You can move parts of the sentence for emphasis or style, for example:

• Pozajmica će početi danas.
• Danas će pozajmica početi.
• Počeće danas pozajmica.

The basic meaning stays the same, but the focus changes a little:

• sentence-final danas is neutral
• sentence-initial Danas gives more emphasis to today
• verb-first Počeće... can sound more marked or stylistic

Yes, you may hear that in spoken Serbian.

That pattern is:

• će da + present tense

So:

• će da počne

This is common in everyday speech in many varieties of Serbian. However, in more standard or formal grammar teaching, learners are usually first taught:

• će + infinitive
• će početi

So the original sentence is a very standard form.

They are similar, but not the same.

• č is a harder sound, roughly like the ch in church
• ć is softer and more palatal

So:

• početi has č
• će has ć

English speakers often pronounce them too similarly at first, which is very common.

Not always.

Pozajmica can refer to a loan or a borrowing, depending on context. It can be used for money, but also more generally for something borrowed.

Depending on the situation, Serbian might also use other words, such as:

• zajam = loan, often more formal
• kredit = credit / bank loan
• pozajmljivanje = borrowing, the act of borrowing

So pozajmica is correct, but the most natural word can depend on context.