Prvi krug počinje sada.

Serbian does not have articles like the or a/an.

So prvi krug can mean:

• the first round
• a first round

Which one is intended depends on context. In this sentence, it will usually be understood as the first round.

Because prvi has to agree with krug.

In Serbian, adjectives change form to match the noun in:

• gender
• number
• case

krug is:

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

So the adjective must also be masculine singular nominative:

• masculine: prvi
• feminine: prva
• neuter: prvo

Example:

• prvi krug = first round
• prva runda = first round
• prvo pitanje = first question

Krug is in the nominative singular.

That is because it is the subject of the sentence — the thing that is beginning.

You can think of the structure as:

• Prvi krug = subject
• počinje = verb
• sada = time expression

So krug stays in nominative because it is doing the action of beginning.

Krug literally means circle, but in many contexts it also means:

• round
• stage
• cycle
• lap

In this sentence, it means round, as in:

• a competition round
• an election round
• a game round
• a selection round

So the exact English translation depends on the situation, but round is the natural meaning here.

Počinje means begins / is beginning / starts.

It is:

• 3rd person singular
• present tense

It matches prvi krug, which is singular:

• krug počinje = the round begins

Compare:

• počinjem = I begin
• počinješ = you begin
• počinje = he/she/it begins
• počinjemo = we begin
• počinjete = you all begin
• počinju = they begin

This is a very common Serbian aspect question.

Serbian verbs often come in aspect pairs:

• počinjati / početi = to begin, to start

Very roughly:

• počinje comes from the imperfective idea
• počne comes from the perfective idea

In many everyday announcements like this one, počinje sada sounds natural and straightforward: begins now / is starting now.

A learner should know that both aspect and context matter a lot in Serbian. In announcements, schedules, narration, and immediate events, Serbian can choose different aspectual forms depending on the speaker’s focus:

• the action as a process or unfolding event
• the action as a single completed starting point

So počinje sada is perfectly normal and idiomatic here.

Sada means now.

Yes, sad also means now. The difference is mostly one of style and rhythm:

• sada = a bit fuller, slightly more formal or neutral
• sad = very common in everyday speech, a bit shorter and more conversational

So you may hear:

• Prvi krug počinje sada.
• Prvi krug počinje sad.

Both are natural.

Yes. Serbian word order is fairly flexible.

The neutral order here is:

• Prvi krug počinje sada.

But you could also hear:

• Sada počinje prvi krug.
• Počinje prvi krug sada. (less neutral, more marked)

The meaning stays basically the same, but the focus changes:

• Prvi krug počinje sada.
  Neutral statement.

• Sada počinje prvi krug.
  More emphasis on now.

Serbian often uses word order to show emphasis, topic, or style rather than changing the basic meaning.

A few sounds in počinje can be tricky for English speakers:

• č = like ch in church, but usually a bit firmer
• nj = like ny in canyon
• j = like English y in yes

So počinje sounds approximately like:

• PO-chee-nye

Not an exact English spelling, but close enough to help.

And the whole sentence is approximately:

• PR-vee kroog PO-chee-nye SA-da

A few more pronunciation notes:

• r in prvi and krug is trilled or tapped
• Serbian stress is not marked in normal writing, so learners usually have to pick it up by listening

Because počinje already means begins / is beginning / starts.

In English, you might say:

• The first round begins now
• The first round is beginning now

Serbian does not need an extra verb like is here, because počinje is the main verb carrying the meaning.

Yes, depending on context.

Because krug has a broad meaning, prvi krug could refer to:

• the first round of a contest
• the first round of voting
• the first lap
• the first cycle or phase

So if you see this sentence by itself, context tells you what kind of round is meant.

Yes. The adjective must agree with the noun.

For example:

• prvi krug
  masculine singular

• prva runda
  feminine singular

• prvo pitanje
  neuter singular

• prvi krugovi
  masculine plural

This agreement is a basic feature of Serbian grammar, and this sentence is a good example of it.