Korisnik sme da uđe u čitaonicu.

In Serbian, modal meanings like may / is allowed to are often expressed with a verb plus da + a present-tense form of another verb.

So here:

• sme = is allowed / may
• da uđe = to enter / that he/she enters

Together, sme da uđe means may enter or is allowed to enter.

This da + present structure is extremely common in Serbian, especially in everyday speech.

Sme comes from the verb smeti.

In this sentence, sme is the 3rd person singular form, so it matches korisnik:

• ja smem = I may / I am allowed
• ti smeš = you may
• on/ona/ono sme = he/she/it may
• mi smemo
• vi smete
• oni smeju

So:

• Korisnik sme... = The user/patron may...

Here it means may or is allowed to.

That is an important distinction:

• moći usually means can / be able to
• smeti usually means may / be allowed to

So compare:

• Korisnik može da uđe. = The user can enter.
  (ability / possibility)
• Korisnik sme da uđe. = The user may enter.
  (permission)

In real life, English often uses can for permission, but Serbian makes this distinction more clearly.

Because ući and ulaziti are two different aspects of the verb:

• ući = to enter, to go in once, as a completed action
• ulaziti = to be entering / to enter habitually or repeatedly

In the sentence Korisnik sme da uđe u čitaonicu, the idea is permission for a single completed act of entering, so ući is the natural choice.

That is why you get:

• da uđe = that he/she enter(s)

If you said da ulazi, it would sound more like is allowed to be entering / to enter repeatedly / to go in regularly, depending on context.

Uđe is the 3rd person singular present form of the perfective verb ući.

That may feel strange to English speakers, because perfective verbs in Serbian can have present-tense forms, but those forms often refer to a future or single complete action depending on the structure.

After da, a perfective present form is very common:

• da uđe = to enter / that he enter
• da dođe = to come
• da uzme = to take

So in this sentence, da uđe is exactly what you would expect after a modal of permission.

Because u can take two different cases, depending on meaning:

• accusative for motion toward / into
• locative for location in / inside

Here the sentence is about movement into the reading room, so Serbian uses the accusative:

• u čitaonicu = into the reading room

Compare:

• Korisnik sme da uđe u čitaonicu. = The user may enter the reading room.
• Korisnik je u čitaonici. = The user is in the reading room.

So:

• čitaonicu = accusative
• čitaonici = locative

Čitaonicu is accusative singular of čitaonica.

The noun čitaonica is a feminine noun ending in -a, and nouns of that type usually form the accusative singular by changing -a to -u:

• žena → ženu
• škola → školu
• čitaonica → čitaonicu

So the ending -u here tells you the noun is the object of motion after u.

Korisnik literally means user. Depending on context, it can also mean:

• user
• customer
• client
• patron

In a library-type context, it often means a library user/patron, not necessarily just a generic user in the computer sense.

So in this sentence, korisnik is probably someone authorized to use the reading room.

Yes, korisnik is grammatically masculine singular.

A specifically feminine form would be korisnica.

So you could say:

• Korisnik sme da uđe u čitaonicu. = A male user / the user may enter...
• Korisnica sme da uđe u čitaonicu. = A female user may enter...

However, masculine forms are often used generically in Serbian, especially in formal or administrative language.

Yes, that is possible.

There are two common ways to express this kind of meaning:

• sme da uđe
• sme ući

In Serbian, the da + present construction is very common and often feels more natural in everyday language. The infinitive version can sound a bit more formal or concise, depending on style and region.

So both are understandable, but sme da uđe is very typical Serbian usage.

Because Serbian does not have articles like a or the.

Whether something means a user, the user, a reading room, or the reading room is understood from context.

So:

• Korisnik can mean a user or the user
• čitaonicu can mean a reading room or the reading room

English requires an article, but Serbian does not.

Yes, Serbian word order is fairly flexible because case endings carry much of the grammatical information.

The neutral order here is:

• Korisnik sme da uđe u čitaonicu.

But other orders are possible for emphasis, for example:

• U čitaonicu korisnik sme da uđe.
  = Into the reading room, the user may enter.
• Korisnik u čitaonicu sme da uđe.
  = The user is allowed to enter the reading room.

These alternatives are grammatically possible, but the original sentence is the most straightforward and neutral.

Yes. The negative is very common:

• ne sme = must not / is not allowed to

For example:

• Korisnik ne sme da uđe u čitaonicu. = The user must not enter the reading room.

This is worth remembering because smeti is often especially common in negative sentences.

So:

• sme = may / is allowed to
• ne sme = must not / is not allowed to

They are directly related.

• čitati = to read
• čitaonica = reading room / reading hall

So čitaonica is literally a place for reading.

This can help you remember the vocabulary:

• čit- = the reading root
• -onica often helps form place nouns

So čitaonica is a room intended for reading or study.