Moja mama rzadko kupuje szminkę, ale zawsze wybiera dobre perfumy na zimę.

Both are possible.

• mama = mom / mother
• moja mama = my mom

In Polish, possessive words like my, your, his, etc. are often omitted when the meaning is obvious, especially with family members. So:

• Mama rzadko kupuje szminkę. = Mom rarely buys lipstick.
• Moja mama rzadko kupuje szminkę. = My mom rarely buys lipstick.

Using moja makes it a little more explicit or emphatic.

Because szminka is the dictionary form, but here it is the direct object of the verb kupować (to buy), so it changes to the accusative case.

• nominative: szminka
• accusative: szminkę

So:

• Kupuje szminkę. = She buys lipstick.

This happens with many feminine nouns ending in -a:

• książka → książkę
• kawa → kawę
• herbata → herbatę

In Polish, perfume is usually expressed as the plural noun perfumy.

So even though English often says perfume as an uncountable singular, Polish normally says:

• perfumy = perfume / perfumes

That is why the adjective is also plural:

• dobre perfumy = good perfume

This is one of those places where Polish and English organize vocabulary differently.

The adjective has to agree with the noun in number, gender, and case.

Here:

• perfumy is plural
• it is also the object of the sentence, but for this noun the accusative plural looks the same as the nominative plural
• so the adjective must also be plural

That gives:

• dobre perfumy

Not:

• dobry perfumy — wrong agreement
• dobra perfumy — wrong agreement

A useful thing to remember is that dobre is often used with non-masculine-personal plural nouns.

Na zimę literally means for winter.

It uses the preposition na plus the accusative case:

• zima = winter
• na zimę = for winter

In this sentence, it means she chooses perfumes that are suitable for the winter season.

Similar examples:

• buty na zimę = shoes for winter
• płaszcz na zimę = a coat for winter
• ubrania na lato = clothes for summer

So na zimę here is very natural and means intended for winter / suitable for winter.

Because the preposition na often requires the accusative case when it means for or indicates direction/target.

So:

• nominative: zima
• accusative: zimę

That is why Polish says:

• na zimę = for winter
• na wiosnę = for spring

This is a very common pattern.

They mean different actions:

• kupuje = buys
• wybiera = chooses / selects

So the sentence is saying:

• she rarely buys lipstick
• but she always chooses good perfume for winter

This suggests that buying and choosing are being contrasted. Maybe she does not often buy lipstick, but when it comes to winter perfume, she is careful and always picks a good one.

Because in Polish, adverbs of frequency often go before the verb, especially in neutral word order.

• rzadko kupuje = rarely buys
• zawsze wybiera = always chooses

This is very natural Polish.

You can sometimes move words around for emphasis, but the sentence as given sounds normal and standard.

Ale means but.

It connects two contrasting ideas:

• Moja mama rzadko kupuje szminkę = My mom rarely buys lipstick
• ale zawsze wybiera dobre perfumy na zimę = but she always chooses good perfume for winter

So the contrast is between rarely and always, and also between lipstick and perfume.

Because Polish often drops subject pronouns when the verb already shows who the subject is.

Here:

• kupuje can mean she buys, he buys, or it buys, depending on context
• wybiera can mean she chooses, he chooses, or it chooses

But since the sentence already starts with Moja mama, we know the subject is she, so Polish does not need to repeat ona.

English usually needs the pronoun:

• My mom rarely buys lipstick, but she always chooses...

Polish usually does not:

• Moja mama rzadko kupuje szminkę, ale zawsze wybiera...

There are other natural ways to express a similar idea.

For example:

• zawsze wybiera perfumy na zimę = she always chooses perfume for winter
• zawsze wybiera dobre zimowe perfumy = she always chooses good winter perfumes
• zawsze wybiera dobre perfumy na sezon zimowy = she always chooses good perfume for the winter season

But the original sentence is completely natural. Perfumy na zimę sounds like perfume suited to winter, while zimowe perfumy sounds a bit more like winter perfumes as a category.

In Polish, szminka is normally a regular countable noun.

So:

• kupić szminkę = to buy a lipstick / to buy lipstick
• dwie szminki = two lipsticks

Even when English uses lipstick in a more general or mass-like way, Polish often still uses the singular countable noun naturally.

So kupuje szminkę is perfectly normal.

A few words that English speakers often find tricky:

• rzadko — the rz sounds like the s in measure or zh
• kupuje — roughly koo-POO-yeh
• szminkę — shmeen-keh, with sz like sh
• wybiera — roughly vih-BYE-ra
• perfumy — per-FOO-mih
• zimę — ZEE-meh

A few sound hints:

• sz = English sh
• rz and ż usually sound similar in modern Polish
• ę at the end of a word is often pronounced approximately like -eh or a nasalized vowel, depending on speech style

The sentence follows a very natural Polish word order:

• Moja mama — subject
• rzadko kupuje — adverb + verb
• szminkę — object
• ale — conjunction
• zawsze wybiera — adverb + verb
• dobre perfumy — object
• na zimę — prepositional phrase

So the structure is basically:

Subject + adverb + verb + object, but + adverb + verb + object + extra phrase

Polish word order is more flexible than English, but this version sounds neutral and idiomatic.