Ta pieczątka jest czerwona, a potwierdzenie dostanę jutro rano.

Because pieczątka is a feminine noun in Polish. Demonstratives must agree with the noun’s gender:

• ten = masculine
• ta = feminine
• to = neuter

So:

• ta pieczątka = this stamp / this seal

This is the same kind of agreement you also see in the adjective czerwona.

Because adjectives in Polish must agree with the noun they describe in gender, number, and case.

Here, pieczątka is:

• feminine
• singular
• nominative

So the adjective also takes the feminine singular nominative form:

• masculine: czerwony
• feminine: czerwona
• neuter: czerwone

That is why we get:

• Ta pieczątka jest czerwona.

Pieczątka usually means a stamp, rubber stamp, or official seal/impression, not a postage stamp on a letter.

So in this sentence it most likely refers to an official stamp or mark on a document.

If you meant a postage stamp, the usual word would be znaczek.

In this kind of sentence, jest is normally required.

• Ta pieczątka jest czerwona. = This stamp is red.

Polish often omits to be in some informal or special contexts, but with a normal adjective predicate like this, jest is the standard form.

So Ta pieczątka czerwona would sound incomplete or nonstandard in ordinary speech.

A often links two clauses while also showing a mild contrast or a shift of topic.

Here:

• Ta pieczątka jest czerwona, a potwierdzenie dostanę jutro rano.

This feels like:

• The stamp is red, and/as for the confirmation, I’ll get it tomorrow morning.

Compare:

• i = simple and
• ale = but, stronger contrast
• a = something between them; often and, while, or whereas, depending on context

So a is very natural here because the sentence moves from one piece of information to another, with a slight contrast in topic.

It is the object of dostanę, but the form happens to stay the same.

Potwierdzenie is a neuter noun. In Polish, many neuter nouns have the same form in the nominative and accusative singular.

So:

• nominative: potwierdzenie
• accusative: potwierdzenie

That is why the object looks unchanged.

Potwierdzenie means confirmation, verification, or sometimes a confirmation document/receipt, depending on context.

In this sentence, it most likely means:

• a confirmation
• or a confirmation document

The exact English wording depends on the situation, but the Polish word is perfectly natural here.

Dostanę looks like a present-tense form, but because dostać is a perfective verb, it refers to the future.

So:

• dostanę = I will get / I will receive

This is a very important Polish pattern:

• imperfective verbs form the future with będę + infinitive / past-like form
• perfective verbs often use present-looking endings to express a simple future

So:

• dostaję = I am getting / I get (imperfective, present)
• dostanę = I will get (perfective, future)

Because the verb ending already tells you the subject.

• dostanę = I will get

In Polish, subject pronouns are often omitted unless you want emphasis, contrast, or clarity.

So both are possible:

• Dostanę jutro rano. = normal
• Ja dostanę jutro rano. = more emphatic, like I will get it tomorrow morning

Omitting ja is the most natural choice here.

Yes, it is a very common expression.

• jutro = tomorrow
• rano = in the morning / morning

Together:

• jutro rano = tomorrow morning

This is a normal and very common way to say it in Polish.

Yes. Polish word order is more flexible than English word order, because endings carry much of the grammatical information.

For example, these are all possible:

• Ta pieczątka jest czerwona, a potwierdzenie dostanę jutro rano.
• Ta pieczątka jest czerwona, a jutro rano dostanę potwierdzenie.
• Potwierdzenie dostanę jutro rano, a ta pieczątka jest czerwona.

They all keep basically the same core meaning, but the emphasis changes.

In your sentence, potwierdzenie comes early in the second clause, which gives it a little prominence.

A few sounds here are especially important for English speakers:

• cz = like ch in chop, but usually a bit harder
• ą = a nasal vowel, often sounding roughly like on/om depending on context
• rz = like the zh sound in measure
• dz in -dzenie = a voiced sound like ds/z combined, depending on position
• nie often sounds like nye

Rough approximations:

• pieczątka ≈ pye-CHONT-ka
• potwierdzenie ≈ pot-vyer-DZE-nye

These are only approximations, but they can help at first.

Yes: Polish stress is usually on the second-to-last syllable of each word.

So roughly:

• pie-CZĄT-ka
• czer-WO-na
• pot-wier-DZE-nie
• dos-TA-nę
• JU-tro
• RA-no

This regular stress pattern is very helpful for learners, because it works for most Polish words.