Jedna parówka została w lodówce, a rogalik z masłem leży na stole.

Because parówka is a feminine noun, so the numeral one must agree with it in gender.

• jeden = masculine
• jedna = feminine
• jedno = neuter

So:

• jeden rogalik
• jedna parówka
• jedno jajko

In Polish, numbers like one behave a bit like adjectives and change form to match the noun.

Parówka means a frankfurter, hot dog sausage, or wiener-type sausage. It usually refers to a soft, processed sausage often eaten hot or cold.

So Jedna parówka is one sausage / one hot-dog-style sausage.

Here została means something like remained, was left, or stayed behind.

So:

• Jedna parówka została w lodówce = One sausage was left in the fridge / One sausage remained in the fridge

This is the past tense, feminine singular form of zostać.

A learner might first know zostać as to become, and that is correct in many contexts, but it also often means to remain or to be left depending on the sentence.

Because the subject is parówka, and parówka is feminine singular.

In the past tense, Polish verbs agree with the subject in gender and number:

• został = masculine singular
• została = feminine singular
• zostało = neuter singular
• zostali / zostały = plural

So:

• parówka została
• rogalik został
• jajko zostało

Because after w meaning in, Polish usually uses the locative case when talking about location.

• dictionary form: lodówka = fridge
• locative singular: w lodówce = in the fridge

This is a very common pattern:

• w domu = in the house
• w szkole = at school / in the school
• w lodówce = in the fridge

So the ending changes because the noun must go into the correct case.

Because the preposition z meaning with takes the instrumental case.

• dictionary form: masło = butter
• instrumental singular: masłem = with butter

So:

• rogalik z masłem = a croissant/roll with butter
• kanapka z serem = a sandwich with cheese
• kawa z mlekiem = coffee with milk

Be careful: z can also mean from, and in that meaning it usually takes a different case. But here it clearly means with.

Rogalik literally means a small crescent-shaped bread or pastry. Depending on context, it can be translated as:

• croissant
• crescent roll
• small crescent pastry

It is a diminutive form, which often makes the word sound smaller, more familiar, or more natural in everyday speech.

So rogalik z masłem is something like a croissant with butter or a buttered crescent roll, depending on context.

Because leżeć means to lie or to be lying physically in a horizontal position.

So:

• rogalik z masłem leży na stole = the buttered roll/croissant is lying on the table = more naturally in English, is on the table

Polish often uses more specific position verbs where English simply uses be:

• książka leży na stole = the book is on the table
• obraz wisi na ścianie = the picture is hanging on the wall
• krzesło stoi w kącie = the chair is standing in the corner

So leży sounds natural because the food item is resting on the table.

Because the sentence combines two ideas:

• Jedna parówka została w lodówce — something happened or turned out to be the case: one sausage was left behind in the fridge.
• a rogalik z masłem leży na stole — the croissant is currently on the table.

This kind of tense combination is normal if the speaker is describing a present situation while also referring to how it came about.

It can feel like:

• One sausage got left in the fridge, and the buttered roll is on the table.

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

Whether something means a sausage, one sausage, or the sausage depends on context, word choice, and sometimes numerals such as jedna.

Here:

• jedna parówka clearly means one sausage
• rogalik z masłem could be understood as a croissant with butter or the croissant with butter, depending on context

Polish speakers do not need articles to make the sentence natural.

Yes, Polish word order is fairly flexible, although some orders sound more natural than others.

This sentence:

• Jedna parówka została w lodówce, a rogalik z masłem leży na stole.

is a neutral, natural order.

You could change it for emphasis, for example:

• W lodówce została jedna parówka...
  This emphasizes in the fridge.
• Na stole leży rogalik z masłem.
  This emphasizes on the table.

So the default order is not the only possible one, but it is a very normal one.

A often translates as and, but it is not exactly the same as i.

In this sentence:

• ..., a rogalik z masłem leży na stole.

a links two pieces of information with a mild contrast or comparison, something like:

• and
• while
• whereas
• and as for...

So the feeling is a bit like:

• One sausage was left in the fridge, while the buttered roll is on the table.

If you used i, it would sound more like simple addition. A is often preferred when comparing two items or locations.

A rough English-friendly guide:

• lodówce ≈ lo-DOOF-tseh
• leży ≈ LEH-zhih

A few useful pronunciation notes:

• ó sounds like u
• w sounds like English v
• c sounds like ts
• ż sounds like the s in measure

So:

• lodówce has the sound cluster -wc-, pronounced roughly -vts-
• leży has ż, a voiced zh sound

These are only approximations, but they are a good start.