Probni rad počinje sutra.

Literally, probni means trial / test / practice, and rad often means work. But in school or testing contexts, probni rad usually means something more natural in English like:

• mock exam
• practice test
• trial test
• sometimes test paper

So yes, the literal pieces are understandable, but the whole phrase is best learned as a set expression used for a practice or trial exam/task.

Because probni has to agree with rad.

In Serbian, adjectives change form to match the noun’s:

• gender
• number
• case

Here:

• rad is masculine
• singular
• nominative (the basic dictionary form, used here as the subject)

So the adjective also takes the masculine singular nominative form:

• probni rad

Compare:

• probni rad = masculine
• probna proba = feminine
• probno pitanje = neuter

Yes, rad often does mean work, but like many nouns, it has a wider range of uses depending on context.

It can refer to:

• work in general
• a piece of written work
• a paper
• an assignment
• a test piece

In educational language, rad can sound like written work, paper, or assignment rather than just work in the broad English sense.

So in probni rad, the word rad is being used in that school/testing sense.

Počinje is the 3rd person singular present tense form of počinjati / početi-related usage, meaning:

• it starts
• it is starting
• it begins

Here it agrees with the singular subject probni rad.

So:

• probni rad počinje = the practice test starts / is starting

The ending -e here is part of the present-tense verb form.

Because Serbian, like English, can use the present tense for a scheduled or arranged future event.

So Probni rad počinje sutra is very natural and means something like:

• The mock exam starts tomorrow
• The practice test begins tomorrow

This is similar to English sentences like:

• The class starts tomorrow.
• The train leaves at six.

The word sutra makes the future time clear.

Yes, absolutely.

Both are correct, but they feel slightly different:

• Probni rad počinje sutra.
  = present tense used for a scheduled future event; very natural and common

• Probni rad će početi sutra.
  = explicit future tense; also correct

The first often sounds a bit more like a timetable or arrangement. The second simply states the future more directly.

Because Serbian does not have articles like a and the.

So Serbian just says:

• Probni rad

and context tells you whether English should use:

• a practice test
• the practice test

In this sentence, English would usually say the because it sounds like a specific scheduled test:

• The practice test starts tomorrow.

But Serbian does not need a separate word for that.

Because sutra is already a time adverb meaning tomorrow.

So Serbian says simply:

• sutra = tomorrow

No preposition like on or at is needed.

This is just like English:

• It starts tomorrow, not It starts on tomorrow.

Yes. Serbian word order is more flexible than English word order.

The neutral order here is:

• Probni rad počinje sutra.

But you could also hear:

• Sutra počinje probni rad.
• Probni rad sutra počinje.

These versions can shift emphasis slightly:

• Sutra počinje probni rad.
  puts more focus on tomorrow

• Probni rad počinje sutra.
  sounds neutral and straightforward

Even though word order can change, not every order sounds equally natural in every situation. The original sentence is a very normal default version.

A rough English approximation is:

• POH-chee-nyeh

A few important sounds:

• č sounds like ch in church
• nj is like the ny sound in canyon or Spanish ñ
• je at the end sounds roughly like yeh

So počinje is not pronounced like plain English po-kin-je or po-sin-je.

Yes, it matters a little.

Serbian verbs often come in aspect pairs:

• počinjati = imperfective
• početi = perfective

In everyday usage, počinje is the natural present form used for is starting / starts in this kind of sentence.

If you use the explicit future with the perfective verb, you get:

• će početi = will start

So a learner should mainly remember this contrast:

• počinje sutra = starts tomorrow
• će početi sutra = will start tomorrow

Both are correct; the first is especially common for scheduled events.

Yes, completely.

It has:

• a subject: probni rad
• a verb: počinje
• a time expression: sutra

So it is a full, natural Serbian sentence meaning that the event begins tomorrow. No extra pronoun is needed, and no article is needed either.