Moj posao počinje u osam sati.

• Moj = my
• posao = job / work
• počinje = starts / begins
• u = at / in
• osam = eight
• sati = hours / o’clock in this time expression

So the structure is very close to English: My job starts at eight o’clock.

Because posao is a masculine singular noun, and the possessive adjective has to agree with it.

So:

• moj = masculine singular
• moja = feminine singular
• moje = neuter singular

Since posao is masculine, you say moj posao.

Because posao is the subject of the sentence, so it stays in the nominative case.

In this sentence, the job/work is the thing that starts, so Serbian uses the basic dictionary form:

• posao = nominative singular

Other forms like posla or poslu would appear in different grammatical roles.

Because the subject posao is third person singular, and the verb has to agree with it.

Here is the pattern:

• ja počinjem = I start
• ti počinješ = you start
• on/ona/ono počinje = he/she/it starts

Since posao is like it, Serbian uses počinje.

Yes. Počinje is grammatically present tense.

Serbian often uses the present tense for:

• regular habits
• schedules
• fixed arrangements

So Moj posao počinje u osam sati can mean:

• My work starts at eight in general
• My work starts at eight as a scheduled fact

This is very similar to English sentences like The train leaves at six.

In Serbian, clock times are commonly expressed with u.

So:

• u osam sati = at eight o’clock
• u pet sati = at five o’clock
• u jedan sat = at one o’clock

Think of u here as the normal preposition used for specific times on the clock.

Because after numbers 5 and higher, Serbian uses a special plural form of sat in time expressions:

• jedan sat = one o’clock / one hour
• dva sata = two o’clock / two hours
• tri sata
• četiri sata
• pet sati
• osam sati

So osam sati is the correct form for eight o’clock.

Yes. That is very common and natural in everyday speech.

Both are correct:

• Moj posao počinje u osam sati.
• Moj posao počinje u osam.

Adding sati is a bit more explicit, but very often Serbian speakers leave it out when the meaning is obvious.

No. You can omit it if the context already makes it clear.

Compare:

• Moj posao počinje u osam sati. = My job starts at eight.
• Posao počinje u osam sati. = The job/work starts at eight, or work starts at eight depending on context.

Using moj adds clarity or emphasis.

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

The neutral version is:

• Moj posao počinje u osam sati.

But you may also hear variations like:

• Posao mi počinje u osam sati.
• U osam sati moj posao počinje.

These can sound more marked, more conversational, or more focused on a particular part of the sentence. The most natural basic version for a learner is still:

• Moj posao počinje u osam sati.

It can mean either, depending on context.

• posao often means job
• it can also mean work in a more concrete everyday sense

So this sentence could be understood as:

• My job starts at eight
• My work starts at eight

If you want to talk specifically about going to work, Serbian might use a different expression, such as:

• Idem na posao u osam. = I go to work at eight.

That is different from saying that the job/work itself starts at eight.

A learner-friendly approximation is:

po-CHEEN-ye

A few useful details:

• č sounds like ch in church
• nj sounds like the ny in canyon or Spanish ñ
• the stress is on the first syllable: POčinje

So the whole sentence is approximately:

Moy PO-sao PO-cheen-ye oo OSam SAtee

That is only an approximation, but it will get you close.

Because Serbian does not have articles like English a and the.

So Serbian simply says:

• posao = job / the job / a job

The exact meaning depends on context.

In this sentence, moj already makes it specific:

• moj posao = my job

So no article is needed.