Osiguravač će proveriti polisu osiguranja.

Because će is a clitic in Serbian. Clitics usually go in the second position in the sentence or clause.

So in Osiguravač će proveriti polisu osiguranja, the first element is osiguravač, and the clitic će comes right after it.

This is very normal Serbian word order:

• Osiguravač će proveriti... = neutral statement

You will also see forms like proveriće in other sentences, where the future marker is attached to the verb:

• Proveriće polisu osiguranja.

Both are related to the future tense.

It is the future tense.

More specifically:

• će = future auxiliary
• proveriti = infinitive of a perfective verb

So će proveriti means something like will check / will verify.

Because proveriti is perfective, it suggests a completed single action: the checking will be carried out and completed. It does not sound ongoing or repeated.

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

• proveriti = perfective = to check, to verify, once, as a completed act
• proveravati = imperfective = to be checking, to check repeatedly, to check in general

In this sentence, the idea is a single future action, so proveriti fits naturally.

Compare:

• Osiguravač će proveriti polisu osiguranja. = The insurer will check the policy.
• Osiguravač će proveravati polisu osiguranja. = The insurer will be checking / will check repeatedly the policy.

Because polisu is the accusative singular form, and it is the direct object of the verb proveriti.

The base form is:

• polisa = policy

But after a transitive verb like proveriti, the direct object usually goes in the accusative:

• polisa → polisu

This is a very common feminine noun pattern:

• knjiga → knjigu
• adresa → adresu
• polisa → polisu

Because osiguranja is in the genitive singular and depends on polisu.

The phrase polisa osiguranja literally means policy of insurance, which in natural English is insurance policy.

So:

• polisa = policy
• osiguranje = insurance
• osiguranja = of insurance

This kind of noun + genitive structure is very common in Serbian.

Osiguravač means insurer.

In insurance language, it usually refers to the party that provides the insurance, often the insurance company or legal insurer.

It is built from the same word family as:

• osiguranje = insurance
• osigurati = to insure / secure
• osiguranik = insured person / policyholder, depending on context
• osiguravač = insurer

So this is a formal, standard word you would expect in contracts, legal language, and business contexts.

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

So Serbian simply says:

• osiguravač
• polisu osiguranja

Whether English uses a or the depends on context, and Serbian usually leaves that unstated.

Learners often want a direct equivalent of the, but Serbian does not normally mark definiteness that way. Context does the work instead.

Yes. Serbian word order is more flexible than English because case endings show what each word is doing.

The neutral order here is:

• Osiguravač će proveriti polisu osiguranja.

But other orders are possible for emphasis, such as:

• Polisu osiguranja će proveriti osiguravač.
• Osiguravač polisu osiguranja će proveriti.
  This is less neutral and more marked.

Even when the order changes, the cases still show:

• osiguravač = subject
• polisu = direct object
• osiguranja = genitive dependent on polisu

So the meaning usually stays the same, but the emphasis changes.

Yes, the meaning is the same. The difference is mainly one of pronunciation standard / regional standard.

• proveriti = Ekavian
• provjeriti = Ijekavian

Likewise:

• će proveriti / će provjeriti

Both are standard in different varieties of Serbian (and closely related standards in the region). If you are learning Serbian used in Serbia, you will often see proveriti.

This sentence contains both sounds:

• č in osiguravač
• ć in će

They are different consonants in Serbian.

A simple learner-friendly approximation:

• č = a harder ch sound, like English ch in chocolate
• ć = a softer sound, somewhere between English t
  • y and a very soft ch

So:

• osiguravač ends with a hard č
• će begins with a soft ć

English does not have a perfect match for ć, so it usually takes practice and listening.

It is in the nominative singular, because it is the subject of the sentence.

The dictionary form is:

• osiguravač

And in this sentence it stays the same because masculine nouns of this type often have the same form in the nominative singular as in the basic dictionary entry.

So the structure is:

• Osiguravač = subject, nominative
• će proveriti = future verb phrase
• polisu osiguranja = object phrase, with accusative + genitive