Mój ojciec wraca z pracy późno.

Because mój has to agree with ojciec in gender, number, and case.

• ojciec is masculine singular
• the sentence uses the nominative case, because ojciec is the subject

So the correct form is:

• mój ojciec = my father

Compare:

• moja matka = my mother
• moje dziecko = my child

So mój / moja / moje work like gender-matching forms of my.

Ojciec is in the nominative case because it is the subject of the sentence — the person doing the action.

In this sentence:

• Mój ojciec = the subject
• wraca = the verb
• z pracy = from work
• późno = late

You may see other forms of ojciec in different sentences, for example:

• Widzę ojca = I see my father
• Mówię o ojcu = I’m talking about my father

But here, since he is the subject, Polish uses ojciec.

Wraca is the 3rd person singular present tense of wracać.

That matches mój ojciec because my father is:

• 3rd person
• singular

So:

• ja wracam = I return / I’m returning
• ty wracasz = you return
• on/ojciec wraca = he / father returns

In this sentence, wraca can mean:

• returns
• comes back

Depending on context, it can also sound habitual, like comes back from work late.

Because wracać and wrócić are different aspects.

• wracać = imperfective
• wrócić = perfective

In the sentence Mój ojciec wraca z pracy późno, the idea is usually a habitual/repeated action, so Polish uses the imperfective verb:

• wraca = comes back / returns (regularly, generally)

By contrast:

• Mój ojciec wróci późno = My father will come back late

So:

• wraca = present, ongoing, repeated, general
• wróci = future completed event

Because the preposition z meaning from/out of requires the genitive case.

The noun praca changes in the genitive singular:

• praca → pracy

So:

• z pracy = from work

This is a very common pattern in Polish:

• z domu = from home
• z Polski = from Poland
• z biura = from the office

So the preposition controls the case, and that is why praca changes form.

Here it means from.

Polish z can mean different things depending on context:

• z pracy = from work
• z ojcem = with my father

The meaning changes with the phrase, and sometimes with pronunciation too. In z pracy, it clearly means from work.

Usually not here. In z pracy, the z is pronounced more like s, because it comes before the voiceless p in pracy.

So it sounds approximately like:

• s PRA-tsy

This kind of voicing change is very common in Polish pronunciation.

Also:

• pracy is roughly PRA-tsy
• c in Polish is like ts

So even though it is written z pracy, you will often hear something closer to s pracy.

Because here Polish needs an adverb, not an adjective.

• późno = late
• późny / późna / późne = late (as an adjective)

In this sentence, późno describes how / when he comes back, so it modifies the verb wraca.

Compare:

• On wraca późno. = He comes back late.
• To jest późny pociąg. = This is a late train.

So:

• use późno with verbs
• use późny/późna/późne with nouns

Yes. Polish present tense often covers both:

• simple present in English
• sometimes present continuous in English

So wraca can mean:

• comes back
• is coming back

However, without extra context, this sentence is most naturally understood as a general/habitual statement:

• My father comes back from work late

If you wanted to make the right now meaning clearer, context would usually do that.

Yes, you could say Ojciec wraca z pracy późno, and it can sound natural in the right context.

Polish often omits possessive words like my, your, his when the relationship is obvious. But with family words, speakers may include them for:

• clarity
• emphasis
• natural style in a particular context

So both are possible:

• Mój ojciec wraca z pracy późno.
• Ojciec wraca z pracy późno.

The version with mój is a bit more explicit: my father.

Because Polish has no articles like a / an / the.

English says:

• my father
• from work
• sometimes from the office

Polish usually expresses definiteness through:

• context
• word order
• case endings
• sometimes demonstratives like ten if needed

So Polish does not need an article here.
Mój ojciec wraca z pracy późno is complete without anything corresponding to the.

Yes. Polish word order is more flexible than English because grammatical roles are often shown by case endings, not just position.

The neutral order here is:

• Mój ojciec wraca z pracy późno.

But other orders are possible, depending on emphasis:

• Mój ojciec późno wraca z pracy.
• Z pracy mój ojciec wraca późno.
• Późno mój ojciec wraca z pracy. — more marked, used for emphasis

Even though these all point to roughly the same basic meaning, the focus changes slightly. The original sentence is a very natural, straightforward version.

They are different case forms of the same noun.

• praca = nominative singular
• pracy = genitive singular (and also some other functions in other contexts)

In this sentence, after z meaning from, Polish uses the genitive, so you get:

• z pracy

This is one of the big differences from English: Polish changes noun endings depending on how the noun functions in the sentence.

A rough pronunciation for an English speaker is:

• Moy OY-chyets VRA-tsa s PRA-tsy POOZH-no

A few useful notes:

• mój sounds roughly like moy
• ojciec is roughly OY-chyets
• wr in wraca starts with a kind of v/r cluster: VRA-tsa
• z pracy is pronounced more like s pracy
• ó sounds like oo
• ż in późno sounds like the s in measure

It does not map perfectly to English sounds, but that approximation is a helpful start.