Budući da je ugovor o radu potpisan, zaposleni radi.

Budući da is a conjunction meaning since, as, or given that.

In this sentence, it introduces the reason: Budući da je ugovor o radu potpisan = Since the employment contract has been signed

It is correct and common, but it sounds a bit more formal or written than jer or pošto.

For example:

• Jer je ugovor potpisan, zaposleni radi.
• Pošto je ugovor potpisan, zaposleni radi.

All of these can mean roughly the same thing here.

Because budući da is a fixed conjunction in Serbian. You should learn it as one unit.

So:

• budući da = since / given that

You generally do not analyze it word by word in normal use. Even though budući by itself can be related to future or being, in this expression budući da simply functions as a conjunction.

Je is the 3rd person singular present form of biti (to be).

Here it helps form a passive/resultative construction:

• ugovor je potpisan = the contract is signed / has been signed

So the structure is:

• ugovor = contract
• je = is/has been
• potpisan = signed

This is very common in Serbian.

Because potpisan and potpisao are different forms with different meanings.

• potpisan = signed as a passive/resultative adjective/participle
• potpisao = signed as an active past form meaning someone signed

Compare:

• Ugovor je potpisan.
  = The contract is signed / has been signed.

• Direktor je potpisao ugovor.
  = The director signed the contract.

So in your sentence, the focus is on the state/result of the contract, not on who signed it.

It can mean either, depending on context.

In many cases, Serbian je + past passive participle can express a present state resulting from a completed action, so English may translate it as:

• is signed
• has been signed

In your sentence, the natural English meaning is usually:

• Since the employment contract has been signed, the employee works / can work

The idea is that the signing has already happened, and now that condition is fulfilled.

Ugovor o radu is the standard expression for employment contract or work contract.

Literally:

• ugovor = contract
• o radu = about work / concerning work

This is the usual legal phrase in Serbian. While radni ugovor might be understandable, ugovor o radu is the normal and idiomatic form.

Radu is in the locative singular because it follows the preposition o.

The preposition o usually takes the locative when it means about or concerning.

So:

• rad = work
• o radu = about work / concerning work

In the full phrase:

• ugovor o radu = contract concerning work = employment contract

This is a good phrase to memorize as a whole.

Here zaposleni is being used as a noun, meaning employee.

It originally comes from an adjective meaning employed, but Serbian often uses adjective forms as nouns when the meaning is clear.

So:

• zaposleni = the employee / an employee
• zaposlena = a female employee
• zaposleni can also mean employees in the plural, depending on context

In this sentence, the verb radi is singular, so here it means the employee.

It is nominative singular, because it is the subject of radi.

Structure:

• zaposleni = subject
• radi = works

So:

• zaposleni radi = the employee works

Because the verb is singular, we know zaposleni is singular here, not plural.

Radi is the 3rd person singular present tense of raditi (to work).

So:

• ja radim = I work
• ti radiš = you work
• on/ona radi = he/she works

Here:

• zaposleni radi = the employee works

Do not confuse this with other forms related to rad (work as a noun). In this sentence, radi is clearly a verb.

The comma separates the subordinate clause from the main clause.

• Budući da je ugovor o radu potpisan = subordinate clause giving the reason
• zaposleni radi = main clause

When the reason clause comes first, Serbian normally uses a comma before the main clause.

So the punctuation works much like in English:

• Since the contract has been signed, the employee works.

Yes. Serbian word order is flexible, although some versions sound more natural than others.

You could also say:

• Zaposleni radi budući da je ugovor o radu potpisan.

That still means the same thing, but putting the reason first often sounds a bit more formal or structured, especially in written language.

The original sentence is perfectly natural, especially in administrative or legal-style language.

It is grammatical and natural, but it sounds somewhat formal or administrative because of expressions like:

• budući da
• ugovor o radu

In everyday speech, people might say something simpler, such as:

• Pošto je potpisan ugovor o radu, zaposleni radi.
• Kad je ugovor potpisan, zaposleni radi.

So the original sentence is especially suitable for formal, legal, or official contexts.