Vatrogasac će ugasiti požar.

Će is the future-tense auxiliary. In this sentence, it marks that the action will happen in the future.

So:

• vatrogasac = firefighter
• će ugasiti = will put out / will extinguish
• požar = fire

This is the normal way to form the Croatian future I tense:

• subject + će + infinitive

For example:

• On će doći. = He will come.
• Ona će raditi. = She will work.

Croatian often forms the future with two parts:

1. a present form of htjeti used as an auxiliary: ću, ćeš, će, ćemo, ćete, će
2. the infinitive of the main verb

So:

• ugasiti = to put out / to extinguish
• će ugasiti = will extinguish

This is different from English, but very normal in Croatian.

With on / ona / ono and many nouns, you often see:

• On će ugasiti požar.
• Vatrogasac će ugasiti požar.

This is a very important Croatian point: aspect.

• gasiti = imperfective
• ugasiti = perfective

In simple terms:

• gasiti focuses on the process: to be putting out, to put out in a general/repeated sense
• ugasiti focuses on completion: to extinguish completely

In Vatrogasac će ugasiti požar, the idea is that the firefighter will successfully put the fire out, so the perfective verb ugasiti is the natural choice.

Compare:

• Vatrogasac će gasiti požar.
  = The firefighter will be putting out the fire / will fight the fire.

• Vatrogasac će ugasiti požar.
  = The firefighter will put the fire out.

Požar is the direct object here, so it is in the accusative case.

However, for many masculine inanimate nouns, the accusative singular is identical to the nominative singular.

So:

• nominative: požar
• accusative: požar

That is why it looks unchanged.

Compare with a masculine animate noun, where accusative usually changes:

• nominative: vatrogasac
• accusative: vatrogasca

Example:

• Vidim vatrogasca. = I see the firefighter.

You know this from both meaning and grammar.

• vatrogasac is in the nominative form, which is typically the subject.
• požar is functioning as the direct object of ugasiti.

Also, semantically it makes sense:

• the firefighter does the action
• the fire receives the action

So:

• Vatrogasac = subject
• će ugasiti = verb phrase
• požar = object

Yes. Croatian word order is more flexible than English.

The neutral order here is:

• Vatrogasac će ugasiti požar.

But other orders are possible, depending on emphasis:

• Požar će ugasiti vatrogasac.
  Emphasizes the firefighter as the one who will put it out.

• Vatrogasac požar će ugasiti.
  Possible, but more marked or stylistic.

Even when the order changes, the cases and context usually still show who is doing what.

Yes, very often.

Croatian is a pro-drop language, which means the subject pronoun is often omitted when it is clear from context or the verb form.

For example:

• Ugasit će požar. = He/She will put out the fire.

However, in your sentence the speaker uses vatrogasac because they want to state explicitly who will do it.

Croatian has no articles like English a/an/the.

So vatrogasac can mean:

• a firefighter
• the firefighter

And požar can mean:

• a fire
• the fire

Which one is meant depends on context.

That is why one Croatian sentence can correspond to different English versions:

• A firefighter will put out a fire.
• The firefighter will put out the fire.

These sounds are often tricky for English speakers.

• ć in će is a soft sound, somewhat like a very soft ty/ch sound.
• č is a harder ch sound, closer to the ch in church.
• ž is like the s in measure or the g in genre.

Roughly:

• će sounds approximately like tyeh / chyeh, depending on accent and how precisely you hear it
• požar is roughly PO-zhar
• vatrogasac is roughly VA-tro-ga-sac

A useful warning: č and ć are different letters in Croatian, and learners should try to notice the difference even if it is hard at first.

Vatrogasac means firefighter.

In older or less gender-neutral English, it could also be translated as fireman, but firefighter is usually the best modern translation.

It is grammatically a masculine noun. A female firefighter can be called:

• vatrogaskinja

So:

• vatrogasac = male firefighter / firefighter
• vatrogaskinja = female firefighter

Yes, they mean the same thing.

Croatian has two common ways to write this future form:

• će ugasiti
• ugasit će

Both mean will extinguish / will put out.

A useful rule:

• when the auxiliary comes before the infinitive, the infinitive stays whole:
  će ugasiti

• when the infinitive comes before the auxiliary, the final -i is usually dropped in writing:
  ugasit će

So these are equivalent:

• Vatrogasac će ugasiti požar.
• Vatrogasac ugasit će požar.

The first one is more neutral and common for learners to start with.

By default, it sounds like one future event:

• The firefighter will put out the fire.

Because the verb is perfective (ugasiti), it strongly suggests a single completed action.

If you wanted a more general or habitual meaning, Croatian would often use different wording, often with the imperfective verb:

• Vatrogasci gase požare. = Firefighters put out fires.
• Vatrogasac će gasiti požar. = The firefighter will be fighting/putting out the fire.

So your sentence most naturally refers to a particular fire being extinguished in the future.