Na klupi je ostalo jedno dugo pero, pa sam ga poslije spremila u knjigu.

Because after na when it means on in the sense of location, Croatian uses the locative case.

• klupa = bench
• na klupi = on the bench

So:

• na stolu = on the table
• na polici = on the shelf
• na klupi = on the bench

If there is movement onto something, Croatian often uses na + accusative instead:

• stavila sam knjigu na klupu = I put the book onto the bench

But here the feather was already there, so it is a location, not movement: na klupi.

Because pero is a neuter noun, and both the number-word and the adjective must agree with it in gender, number, and case.

• pero = neuter singular
• jedno = neuter form of one
• dugo = neuter form of long

Compare:

• jedan dugi štap = one long stick (masculine)
• jedna duga olovka = one long pencil (feminine)
• jedno dugo pero = one long feather (neuter)

So the forms are matching pero.

This is the perfect tense of ostati = to remain / to be left.

The perfect tense is formed with:

• the auxiliary biti in the present tense
• plus the past participle

Here:

• je = has/is (3rd person singular auxiliary)
• ostalo = past participle, neuter singular, agreeing with pero

So literally it is something like:

• je ostalo = has remained / was left

The participle is ostalo because the thing that remained is jedno dugo pero, which is neuter singular.

Compare:

• ostao je kaput = a coat was left (masculine)
• ostala je knjiga = a book was left (feminine)
• ostalo je pero = a feather was left (neuter)

Because it agrees with pero, which is neuter singular.

In Croatian past participles often show gender:

• ostao = masculine singular
• ostala = feminine singular
• ostalo = neuter singular

Since pero is neuter, you get ostalo.

Pa is a very common connector. Here it means something like:

• so
• and then
• therefore
• so then

In this sentence it links the two actions naturally:

• first, the feather was left on the bench
• then, the speaker put it into a book

It is slightly more conversational and flowing than a simple i (and).

Ga is the unstressed pronoun meaning it/him in the accusative, and here it refers back to pero.

So:

• pero = the feather
• ga = it

Even though pero is neuter, Croatian uses ga as the accusative singular clitic for that pronoun here.

So:

• spremila sam pero = I put away the feather
• spremila sam ga = I put it away

Using ga avoids repeating pero.

Because sam and ga are clitics. Croatian clitics usually come very early in the sentence or clause, typically in the second position.

So in:

• pa sam ga poslije spremila

the clitic group sam ga comes right after the first element pa.

This is very normal Croatian word order.

A learner should get used to forms like:

• onda sam ga vidjela
• jučer sam joj pisao
• pa sam ih uzela

The clitics often feel “pulled forward” compared with English.

Spremila is the past participle of spremiti and it is in the feminine singular form.

That tells you the speaker is female.

In Croatian, in the past tense, the speaker’s gender is shown:

• spremio sam = I put away / stored (male speaker)
• spremila sam = I put away / stored (female speaker)

So this sentence was said by a woman or girl.

Spremiti is a very useful verb with meanings like:

• to put away
• to store
• to tuck
• to place somewhere safely

In this sentence, because of u knjigu, it has the sense of:

• I tucked it into a book
• I put it into a book

So it is not just random movement. It suggests putting something somewhere intentionally, often neatly or for safekeeping.

Poslije means:

• later
• afterwards

It tells you the second action happened some time after the first one.

So the sequence is:

1. the feather was left on the bench
2. later, the speaker put it into a book

You may also see the similar word kasnije, which often also means later.

Because u can take two different cases depending on the meaning:

• u + accusative = movement into
• u + locative = location in

Here there is movement: the speaker put the feather into a book, so Croatian uses the accusative:

• u knjigu = into the book

Compare:

• Pero je u knjizi. = The feather is in the book. (location: locative)
• Spremila sam pero u knjigu. = I put the feather into the book. (movement: accusative)

This is a very important pattern in Croatian.

Because knjiga is a feminine noun, and after u with movement we need the accusative singular.

• nominative: knjiga
• accusative: knjigu

So:

• u knjigu = into a book / into the book

This is a regular feminine accusative ending:

• škola → školu
• torba → torbu
• knjiga → knjigu

Here, pero means feather, not pen.

Although English speakers may think of pen, in modern Croatian:

• pero usually means feather
• pen is usually olovka or more specifically kemijska olovka

Also, the context strongly points to feather:

• dugo pero = a long feather
• spremila u knjigu = tucked into a book

That sounds like a feather being used as a bookmark or being kept inside a book.

Croatian has no articles.

So a noun like pero can mean:

• a feather
• the feather

The exact meaning depends on context.

In this sentence, English might translate it with a the first time it is mentioned:

• a long feather

Then later with it, because now it has already been introduced.

Croatian does all that without articles.

Yes, ostati is generally a perfective verb, and here it fits well because the sentence presents the result: the feather ended up being left on the bench.

Croatian often uses a perfective verb when the situation is seen as a complete event or resulting state.

A rough contrast would be:

• ostajati = imperfective, repeated/ongoing remaining
• ostati = perfective, to remain / to be left as a completed fact

Here the sentence is about one specific completed situation, so ostalo je is natural.

Yes, but it would sound a bit different.

• poslije = later / afterwards
• nakon toga = after that

Both can work in many contexts, but poslije is shorter and very natural here. It sounds smooth and everyday.

So:

• pa sam ga poslije spremila u knjigu
• pa sam ga nakon toga spremila u knjigu

Both are possible, but the first feels simpler and more conversational.

Croatian word order is flexible. The sentence starts with the location:

• Na klupi = on the bench

Then comes the verb:

• je ostalo

Then the thing being talked about:

• jedno dugo pero

This order helps present the scene naturally: first the place, then what was there.

A more neutral alternative like Jedno dugo pero ostalo je na klupi is also possible, but it shifts the emphasis a bit. Croatian often moves parts around for focus or style.

Yes, very possibly.

Literally it means the speaker put the feather into a book, but in context it can easily suggest:

• tucking it between the pages
• keeping it there
• perhaps using it as a bookmark

Croatian itself does not force that interpretation, but the image is quite natural.