Serviser će instalirati rezervni deo.

Because će is a clitic, and clitics in Serbian usually go in the second position of the clause.

So the neutral pattern here is:

Serviser | će | instalirati rezervni deo.

A native English speaker may expect something like Serviser instalirati će..., but that is not the normal Serbian order.

This second-position rule is very common with short unstressed words like sam, je, ga, se, će, etc.

It is the future tense: Future I.

It is formed with:

• a short form of hteti (ću, ćeš, će, ćemo, ćete, će)
• plus the infinitive of the main verb

So here:

• će = will
• instalirati = to install

Together, će instalirati means will install.

That is how this future tense is commonly built in Serbian.

You use:

• ću/ćeš/će...
• • infinitive

Examples:

• Ja ću doći.
• Oni će raditi.
• Serviser će instalirati rezervni deo.

There is also another common written form when the future auxiliary comes after the verb, where the verb and auxiliary join together, for example instaliraće. But in your sentence, the normal structure is će instalirati.

Because rezervni deo is the direct object of the sentence, so it is in the accusative case.

However, for masculine inanimate nouns, the accusative singular is the same as the nominative singular.

So:

• nominative: rezervni deo
• accusative: rezervni deo

That is why it looks unchanged.

Compare that with a masculine animate noun:

• nominative: serviser
• accusative: servisera

So Serbian does mark case, but not every noun changes in every situation.

Because adjectives in Serbian usually come before the noun they describe.

So:

• rezervni deo = spare part
• novi auto = new car
• dobar film = good movie

Also, the adjective must agree with the noun in:

• gender
• number
• case

Here both words are masculine singular accusative/nominative in form:

• rezervni
• deo

It is grammatical and understandable, but depending on context, a native speaker might choose a different verb.

For a spare part, Serbian often uses:

• ugraditi = to install/fit into something
• zameniti = to replace
• montirati = to mount/assemble

So if the idea is that the technician will fit a replacement part into a machine, Serviser će ugraditi rezervni deo may sound more natural in many situations.

Still, instalirati is not wrong, especially in technical or modern usage.

Serviser usually means a service technician, repair technician, or maintenance worker.

It is someone who services, repairs, installs, or maintains equipment.

Depending on context, English might translate it differently:

• technician
• repairman
• service engineer
• maintenance worker

So it is a practical job word, not just a direct one-to-one equivalent of a single English term.

Because Serbian does not have articles like English.

So serviser can mean:

• a technician
• the technician

And rezervni deo can mean:

• a spare part
• the spare part

The exact meaning depends on context, not on an article.

This is something English speakers often need time to get used to.

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

Your sentence is the most neutral and straightforward order: Serviser će instalirati rezervni deo.

Other orders are possible, but they usually change the emphasis:

• Rezervni deo će instalirati serviser.
  This puts more focus on rezervni deo or contrasts who will install it.
• Serviser će rezervni deo instalirati.
  Also possible, but less neutral and more marked.

For learners, the version you have is the best default pattern.

A rough guide is:

• će: something like tyeh, with a soft sound at the beginning
• deo: DEH-oh, in two syllables

A few notes:

• ć is softer than English ch
• č and ć are different sounds in Serbian
• deo is not one syllable; say both vowels clearly

So the whole sentence is roughly: SEHR-vee-ser tyeh een-stah-LEE-rah-tee REH-zerv-nee DEH-oh

That is only an approximation, but it can help at the beginning.

Yes, basically.

deo is the standard Ekavian Serbian form.
dio is the Ijekavian form used in other standards and regions, especially in Croatian, Bosnian, and Montenegrin, and in some Serbian usage as well.

So:

• rezervni deo
• rezervni dio

Both mean the same thing; the difference is mainly regional/standard variety.