To jest mój dziesiąty dzień w nowej pracy.

Yes—to jest literally means this is / it is.

In this sentence, To jest mój dziesiąty dzień w nowej pracy is a very natural way to say This is my tenth day at/in my new job.

A few useful points:

• to = this / it
• jest = is
• In everyday speech, jest is often omitted here:
  • To mój dziesiąty dzień w nowej pracy.
• That shorter version is also very natural.

So both are correct:

• To jest mój dziesiąty dzień w nowej pracy.
• To mój dziesiąty dzień w nowej pracy.

Because mój has to agree with dzień.

In Polish, possessive words like my change form depending on the gender, number, and case of the noun they describe.

Here:

• dzień = a masculine singular noun
• so my must be in the masculine singular nominative form
• that form is mój

Compare:

• mój dzień = my day (masculine)
• moja praca = my job/work (feminine)
• moje biuro = my office (neuter)

So mój dziesiąty dzień is correct because both words describe dzień.

Because Polish uses an ordinal number here, not a cardinal number.

• dziesięć = ten
• dziesiąty = tenth

In English, the sentence is my tenth day, not my ten day, so Polish does the same thing:

• mój dziesiąty dzień = my tenth day

This is different from saying ten days:

• dziesięć dni = ten days
• dziesiąty dzień = the tenth day

That distinction is very important in Polish.

It is singular because dziesiąty dzień means tenth day, not ten days.

With ordinal numbers, Polish treats the phrase like an adjective + noun combination:

• pierwszy dzień = first day
• drugi dzień = second day
• dziesiąty dzień = tenth day

So the noun stays singular.

Compare:

• To jest mój dziesiąty dzień. = This is my tenth day.
• Pracuję tu dziesięć dni. = I’ve been working here for ten days.

So:

• ordinal number → singular noun
• cardinal number → often a different number/case pattern, such as dziesięć dni

Dzień is in the nominative singular.

That is because the sentence is an identifying/equational sentence:

• To jest mój dziesiąty dzień...
• literally: This is my tenth day...

The phrase mój dziesiąty dzień functions as the thing being identified, so nominative is expected.

You can think of it similarly to:

• To jest mój brat. = This is my brother.
• To jest nowy samochód. = This is a new car.

In all of these, the noun phrase after to jest is nominative.

After w meaning in / at a location or state, Polish normally uses the locative case.

So:

• w pracy = at work / in work
• w nowej pracy = in the new job / at the new job

Here, praca is a feminine noun, and in the singular locative it becomes pracy.

So the pattern is:

• nominative: nowa praca
• locative after w: w nowej pracy

This use of w is very common when talking about being in a place, situation, institution, or role.

Because adjectives in Polish must agree with the noun they describe in:

• gender
• number
• case

The noun is praca, which is:

• feminine
• singular
• in this sentence, locative (because of w)

So nowa changes to the feminine singular locative form:

• nowa praca = a new job (nominative)
• w nowej pracy = in the new job (locative)

This is the same pattern you see in other phrases:

• w polskiej szkole = in the Polish school
• w dobrej restauracji = in a good restaurant

It can suggest either, depending on context, but here job is the best natural translation.

• praca can mean work in a general sense
• it can also mean job/employment/position

In w nowej pracy, the meaning is usually:

• in my new job
• at my new job

So although the word is the same, English usually chooses job here because we are talking about a specific new place of employment, not the general idea of work.

Yes, if the context already makes it clear that it is your new job.

The Polish sentence literally says:

• in a/the new job

But in real use, mój does not need to be repeated because mój dziesiąty dzień already strongly suggests we are talking about my new job.

So natural English often becomes:

• This is my tenth day at my new job.

Polish often avoids repeating possessives when the meaning is obvious.

If you wanted to make it fully explicit, you could also say:

• To jest mój dziesiąty dzień w mojej nowej pracy.

But that sounds heavier and is usually unnecessary.

The basic word order here is very natural, but Polish word order is more flexible than English.

Standard, neutral order:

• To jest mój dziesiąty dzień w nowej pracy.

Possible alternatives include:

• To mój dziesiąty dzień w nowej pracy.
• W nowej pracy to jest mój dziesiąty dzień.
• Mój dziesiąty dzień w nowej pracy — to jest dziś.
  (more marked/stylistic)

Even when the order changes, the endings help show the grammatical relationships.

Still, for a learner, the safest and most natural version is the original one.

Yes, that is grammatically correct.

However, Jest to... sounds a bit more formal, written, or emphatic than To jest....

Compare:

• To jest mój dziesiąty dzień w nowej pracy.
  neutral, everyday
• Jest to mój dziesiąty dzień w nowej pracy.
  slightly more formal or deliberate

In normal conversation, To jest... or simply To... is usually more natural.

This part is tricky for English speakers, especially because of dzi, ń, and ą.

A rough guide:

• dziesiąty ≈ דזשESH-on-tih / דזשESH-yon-tih
• dzień ≈ jeny with a soft final ń, though that is only an approximation

A few pronunciation notes:

• dzi is a soft sound, somewhat like j in some contexts, but lighter/palatalized
• ą before t is often pronounced something like on
• dzień ends with ń, a soft n sound, not a hard English n

If you want a practical learner approximation, try:

• dziesiąty dzień ≈ JESH-on-tih jenyń

Not perfect, but good enough as a starting point. The best next step is to hear it spoken by native speakers and imitate the rhythm.

Yes. In Polish, both the possessive adjective and the ordinal number agree with the noun.

Here the noun is dzień, which is:

• masculine
• singular
• nominative

So both words must match that:

• mój = masculine singular nominative
• dziesiąty = masculine singular nominative
• dzień = masculine singular nominative

That is why the whole phrase is:

• mój dziesiąty dzień

If the noun changed, the forms would change too. For example, with the feminine noun praca:

• moja dziesiąta praca = my tenth job

So agreement is happening across the whole noun phrase.

Yes, absolutely. It sounds natural.

A speaker might say it when talking about a recently started job, for example:

• To jest mój dziesiąty dzień w nowej pracy, więc jeszcze wszystkiego się uczę.
  This is my tenth day at my new job, so I’m still learning everything.

Very natural everyday variants would be:

• To mój dziesiąty dzień w nowej pracy.
• Mam dopiero dziesiąty dzień w nowej pracy.
  slightly different structure, more like It’s only my tenth day at my new job
• Dzisiaj jest mój dziesiąty dzień w nowej pracy.
  Today is my tenth day at my new job

So the original sentence is correct, natural, and useful.