Kupiłam nową obrożę dla psa, a stara leży teraz obok drzwi.

Kupiłam tells you the speaker is female.

In the Polish past tense, the verb agrees with the speaker’s gender in the singular:

• kupiłam = I bought (said by a woman)
• kupiłem = I bought (said by a man)

So this sentence is being said by a female speaker.

Because obrożę is the direct object of kupiłam (I bought), so it has to be in the accusative case.

The base form is:

• nowa obroża = a new collar

But in the accusative singular feminine, it changes to:

• nową obrożę

So:

• Kupiłam nową obrożę = I bought a new collar

This is a normal case ending change for many feminine nouns ending in -a.

• nominative: obroża
• accusative: obrożę

Since buy takes a direct object, Polish uses the accusative here.

So the pattern is similar to:

• mam książkę = I have a book
• widzę kobietę = I see a woman
• kupiłam obrożę = I bought a collar

Because the preposition dla always requires the genitive case.

The noun changes like this:

• pies = dog (dictionary form / nominative)
• psa = dog in the genitive

So:

• dla psa = for a dog / for the dog

This is a very important pattern to remember:

• dla + genitive

It can mean either, depending on context.

Polish does not have articles like a and the, so psa by itself does not tell you whether the meaning is definite or indefinite.

So:

• dla psa can mean for a dog
• or for the dog

You understand which one is meant from the situation.

Polish often leaves out a noun when it is already obvious from context.

Here, stara means:

• the old one
• more literally: the old [collar]

The full version would be:

• a stara obroża leży teraz obok drzwi

But Polish very naturally omits obroża here because it was already mentioned.

Here a is a conjunction connecting two clauses. It often means something like:

• and
• while
• but (a mild contrast)

In this sentence, there is a contrast between the new collar and the old one:

• Kupiłam nową obrożę dla psa, a stara leży teraz obok drzwi.
• I bought a new collar for the dog, and the old one is now lying next to the door.

It is not as strong as ale (but), but it does show contrast.

Leży comes from leżeć, which means to lie or to be lying.

So leży is more specific than jest:

• jest = is
• leży = is lying / is lying there

For an object like a collar, Polish often uses leżeć when it is physically resting somewhere.

So:

• stara leży obok drzwi = the old one is lying next to the door

Because obok requires the genitive case.

So the structure is:

• obok + genitive = next to / beside

The noun here is drzwi (door), and its genitive form is also drzwi.

So:

• obok drzwi = next to the door

Because drzwi is a plural-only noun in Polish. This is called plurale tantum.

Even when English uses singular door, Polish normally says drzwi, which is grammatically plural.

That is why you get forms like:

• te drzwi = this door / these doors
• obok drzwi = next to the door

So yes, it looks plural, but it often refers to a single door in English.

Yes, Polish word order is quite flexible.

This sentence has a natural, neutral order:

• stara leży teraz obok drzwi

But other orders are possible, depending on emphasis, for example:

• stara teraz leży obok drzwi
• teraz stara leży obok drzwi

They all mean roughly the same thing, but the focus changes slightly.

Polish uses word order more for emphasis and information flow than English does.

Because Polish has no articles.

English distinguishes between:

• a new collar
• the old collar

Polish does not use separate words for a or the. Instead, definiteness is understood from context.

So:

• nową obrożę can mean a new collar or the new collar
• stara here is understood as the old one because the context makes it clear

Because kupiłam is perfective, and it presents the action as completed.

• kupiłam = I bought / I have bought (completed action)
• kupowałam = I was buying / I used to buy / I bought in an ongoing or repeated sense

In this sentence, the speaker means a finished action: she bought the collar, and now the old one is by the door. That is why kupiłam is the natural choice.

Yes, it is very natural.

It sounds like normal everyday Polish and includes several common features of the language:

• gender in the past tense: kupiłam
• accusative object: nową obrożę
• dla + genitive: dla psa
• omitted repeated noun: stara
• flexible but natural word order
• a plural-only noun: drzwi

So it is a very good example sentence for learners.