Korisnik će se učlaniti u biblioteku.

This is how the future tense is normally built in Serbian:

• će = the future auxiliary, roughly will
• učlaniti se = the main verb, to join / become a member

So:

• Korisnik će se učlaniti = The user will join / will become a member

In Serbian, short words like će and se are clitics, and they usually appear in a fixed position near the beginning of the clause rather than staying tightly attached to the verb the way English words do.

Here se is part of the verb učlaniti se.

Although se often has a reflexive flavor, in this sentence you should mainly learn učlaniti se as a whole expression meaning:

• to become a member
• to sign up
• to join

So it is best to memorize:

• učlaniti se u biblioteku = to join the library

If you remove se, the sentence would not sound correct for this meaning.

Učlaniti se means to become a member of something.

Common examples:

• učlaniti se u biblioteku = join the library
• učlaniti se u klub = join a club
• učlaniti se u stranku = join a political party

It is more specific than a general English join. It usually implies membership.

Because Serbian distinguishes between:

• movement toward/into a place → u + accusative
• location in a place → u + locative

Here the idea is joining/enrolling into the library, so Serbian uses u biblioteku.

Compare:

• Učlaniće se u biblioteku. = He/She will join the library.
• On je u biblioteci. = He is in the library.

So:

• biblioteku = accusative
• biblioteci = locative

Because u here requires the accusative case when it expresses motion toward something.

The noun biblioteka is feminine singular, and its accusative singular form is:

• biblioteka → biblioteku

This is a very common pattern for feminine nouns ending in -a:

• škola → školu
• prodavnica → prodavnicu
• biblioteka → biblioteku

Korisnik literally means user.

Depending on context, it can mean:

• a user of a service
• a customer
• a client
• a beneficiary
• sometimes a patron or account holder

In this sentence, it likely means the user / patron / person using the service who will become a member of the library.

So the exact English translation can vary by context, but user is the basic meaning.

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

So:

• korisnik can mean a user or the user
• biblioteka / biblioteku can mean a library / the library

Which one is intended depends on context.

That means:

• Korisnik će se učlaniti u biblioteku.

could be understood as:

• The user will join the library
• or A user will join a/the library

In practice, context usually makes it clear.

It is in the future tense.

The structure is:

• će
  • infinitive-like verb form in standard usage with clitics

Here:

• će = will
• učlaniti se = join / become a member

So the whole sentence means something that will happen in the future.

A related point: učlaniti se is a perfective verb, which suits a one-time completed action such as joining.

Učlaniti se is perfective, meaning it presents the action as a completed whole:

• joining the library
• becoming a member

That makes sense because joining is usually seen as a single completed event.

The imperfective counterpart is usually:

• učlanjivati se

This would be used in contexts like repetition, process, or habitual meaning, though it is less common in simple everyday statements about joining once.

Compare:

• Učlaniće se u biblioteku. = He/She will join the library.
• Ljudi su se tada masovno učlanjivali u biblioteku. = People were joining the library in large numbers then.

Yes. Serbian word order is more flexible than English, although not completely free.

The neutral order here is:

• Korisnik će se učlaniti u biblioteku.

But other orders are possible for emphasis or style, for example:

• U biblioteku će se učlaniti korisnik.
• Korisnik se neće učlaniti u biblioteku. (with negation)
• Kada će se korisnik učlaniti u biblioteku?

Still, the clitics će and se tend to stay in their usual clitic position, so you cannot move them around completely arbitrarily.

No, not for this meaning.

You need:

• učlaniti se u biblioteku

Without se, the sentence is not correct for become a member / join.

So learn the verb together with se:

• učlaniti se
• not just učlaniti

Yes, this can be a small vocabulary trap.

In Serbian:

• biblioteka = library
• knjižara = bookstore / bookshop

So if you want to say someone is joining a library, biblioteka is correct.

Do not confuse it with a place where books are sold:

• knjižara = bookstore

A rough pronunciation guide is:

• Korisnik ≈ KO-rihs-neek
• će ≈ something like chyeh, with a softer ć sound
• se ≈ seh
• učlaniti ≈ oo-chLAH-nee-tee
• u biblioteku ≈ oo bee-blee-oh-TEH-koo

A few sound notes:

• č is like ch in chocolate
• ć is softer than č
• lj is a single Serbian sound, somewhat like the lli in million for many learners

You do not need a perfect accent right away, but it helps to notice the difference between č and ć.