Nagle okazało się, że to sąsiadka, która przyszła pożyczyć cukier.

Nagle means suddenly or all of a sudden.

It is an adverb, and putting it at the beginning is very natural in Polish when you want to set the scene first:

• Nagle okazało się... = Suddenly it turned out...

Polish word order is flexible, so nagle could appear elsewhere, but sentence-initial position is the most straightforward here.

Okazało się comes from okazać się, which means:

• to turn out
• to prove to be
• to be revealed as

So okazało się, że... is a very common Polish pattern meaning:

• it turned out that...

The się is part of the verb here. You should learn okazać się as one unit, not as okazać plus a separately meaningful się.

Because this is an impersonal structure.

In English, we say:

• it turned out that...

That it does not refer to a real thing; it is just a grammatical placeholder. Polish often handles this by using the neuter singular past form:

• okazało się
• wydawało się
• zdarzyło się

So okazało się, że... is the natural Polish equivalent of it turned out that...

Że means that and introduces a subordinate clause.

So:

• okazało się, że... = it turned out that...

In English, that is often optional:

• It turned out (that) it was the neighbor...

In Polish, że is much more normally expressed, so leaving it out here would sound wrong.

This is a very common point of confusion.

In Polish, to can be used in identification sentences:

• To sąsiadka. = It’s the neighbor.
• To moja siostra. = It’s my sister.

So to is not just ordinary that here. It works as part of an identifying structure.

That is why że to sąsiadka can mean:

• that it was the neighbor
• that it was the female neighbor

Polish often does not need an explicit jest in this kind of sentence.

A more explicit version with a past tense verb is also possible in some contexts:

• że to była sąsiadka

But the shorter że to sąsiadka is very natural.

Because it is the noun being used to identify who the person was.

In a sentence like:

• To sąsiadka

the noun after to is normally in the nominative case.

Also, sąsiadka specifically means a female neighbor. The masculine form would be:

• sąsiad = male neighbor

So the sentence tells you the person was a woman.

Because in Polish, relative clauses introduced by words like który / która / które are separated by commas.

So:

• sąsiadka, która przyszła...

needs a comma.

This is different from English, where commas depend on whether the clause is restrictive or non-restrictive. In Polish, with który-type relative clauses, the comma is standard.

Która refers back to sąsiadka.

It must match sąsiadka in gender and number:

• sąsiadka = feminine singular
• therefore która = feminine singular

It is also the subject of the relative clause:

• która przyszła... = who came...

If the grammar of the relative clause were different, the form of która could change.

Przyszła is the past tense feminine singular form of przyjść (to come).

It is feminine singular because it agrees with sąsiadka:

• sąsiadka ... przyszła

Compare:

• sąsiad przyszedł = the male neighbor came
• sąsiadka przyszła = the female neighbor came

Also, przyjść is perfective, so przyszła presents the action as completed: she came.

Because Polish often uses a verb of motion + infinitive to express purpose.

So:

• przyszła pożyczyć cukier = she came to borrow sugar

This works much like English came to borrow.

The infinitive pożyczyć tells you the purpose of her coming.

Another possible Polish way to express a similar idea would be:

• przyszła po cukier = she came for sugar

But that is a slightly different structure.

This is a very good question, because pożyczyć can be ambiguous if you only look at the dictionary.

Depending on context, it can mean:

• to borrow
• to lend

The sentence makes it clear that the neighbor came to borrow sugar, not to lend it.

Polish usually makes the direction clear through context or extra words, for example:

• pożyczyć coś komuś = to lend something to someone
• pożyczyć coś od kogoś = to borrow something from someone

So here, since the neighbor came asking for sugar, pożyczyć cukier is understood as borrow sugar.

Cukier is the direct object of pożyczyć, so it is in the accusative case.

However, cukier is a masculine inanimate noun, and in the singular its accusative form looks the same as its nominative form:

• nominative: cukier
• accusative: cukier

So the case is accusative, even though the word does not visibly change.

Yes. Polish word order is fairly flexible, but different orders change the emphasis.

The given version is natural and neutral:

• Nagle okazało się, że to sąsiadka, która przyszła pożyczyć cukier.

You could rearrange parts in some contexts, but the original is a good standard model for learners.

In Polish, word order often helps show:

• what is new information
• what is being emphasized
• what is already known from context

So even when another order is grammatically possible, it may not sound as natural in the same situation.