Gdy szyba jest sucha, wycieraczki nie są potrzebne.

Gdy means when in the sense of whenever / when the situation is that... It introduces a subordinate clause.

In this sentence:

• Gdy szyba jest sucha = When the window/windshield is dry

You can often use gdy and kiedy in similar sentences, and both can mean when. But:

• gdy often sounds a bit more neutral or slightly more formal in written Polish
• kiedy is also very common in everyday speech

So this sentence could also be:

• Kiedy szyba jest sucha, wycieraczki nie są potrzebne.

That would still be natural.

Szyba literally means a pane of glass or window glass. Depending on context, it can refer to:

• a window pane
• a car window
• a windshield

In a sentence with wycieraczki (windshield wipers / wipers), the natural interpretation is usually the windshield.

So although szyba by itself is broader than English windshield, the context makes the intended meaning clear.

Because sucha has to agree with szyba.

In Polish, adjectives change form to match the noun’s:

• gender
• number
• case

Here:

• szyba is feminine singular
• so the adjective must also be feminine singular
• therefore: sucha

Compare:

• suchy = masculine singular
• sucha = feminine singular
• suche = neuter singular or non-masculine-personal plural

So:

• sucha szyba = a dry window/windshield

Polish usually uses the verb być (to be) in the present tense, unlike Russian, where it is often omitted.

So:

• szyba jest sucha = the windshield is dry

You normally need jest here.

If you said only:

• Gdy szyba sucha...

that would sound incomplete or very nonstandard in ordinary modern Polish.

Because windshield wipers are normally thought of as a pair, and Polish uses the plural noun wycieraczki.

Singular:

• wycieraczka = a wiper / a wiping device

Plural:

• wycieraczki = wipers

This is similar to English, where we often say the wipers rather than the wiper system.

Because potrzebne here is an adjective meaning needed / necessary.

So:

• wycieraczki nie są potrzebne = the wipers are not needed

Structure:

• nie są = are not
• potrzebne = needed / necessary

By contrast, potrzebują is a verb meaning they need, which would create a completely different sentence:

• Wycieraczki nie potrzebują... = The wipers do not need...

That is not the meaning here.

Again, this is agreement.

The noun wycieraczki is plural, but it is not masculine personal. In Polish, plural adjectives have different forms depending on whether the group is masculine-personal or not.

• potrzebni = masculine-personal plural, for groups of men / male persons
• potrzebne = non-masculine-personal plural

Since wycieraczki are things, not people, you use:

• potrzebne

So:

• wycieraczki są potrzebne = the wipers are needed

Yes, Polish word order is more flexible than English, because endings carry a lot of grammatical information.

The neutral order here is:

• Wycieraczki nie są potrzebne.

But other orders are possible for emphasis, for example:

• Nie są potrzebne wycieraczki.
• Potrzebne nie są wycieraczki. (more marked)

The original order sounds the most straightforward and natural in standard usage.

Because Gdy szyba jest sucha is a subordinate clause, and in Polish subordinate clauses are normally separated by a comma.

So:

• Gdy szyba jest sucha, wycieraczki nie są potrzebne.

This is standard punctuation.

In English, the comma is also normal when the when-clause comes first.

Usually not in this context.

• okno = window
• szyba = glass pane / car window / windshield

With wycieraczki, Polish strongly prefers szyba, because wipers clean the glass, especially the windshield, not the window in the general architectural sense.

A more explicit option would be:

• przednia szyba = front windshield / windscreen

So you could say:

• Gdy przednia szyba jest sucha, wycieraczki nie są potrzebne.

A rough English-friendly guide:

• Gdy ≈ gdi
• szyba ≈ SHI-ba
• jest ≈ yest
• sucha ≈ SU-ha (with ch like Scottish loch or German Bach)
• wycieraczki ≈ vuh-chye-RACH-kee
• nie ≈ nyeh
• są ≈ sow but nasalized
• potrzebne ≈ po-CHEB-neh

A few key sounds:

• sz = sh
• cz = ch as in chop
• wy- often sounds roughly like vuh / vi
• ą is a nasal vowel; before pauses it often sounds a bit like on/ow with nasal coloring

Both work.

• needed is often the most direct translation in this sentence
• necessary is slightly more formal

So these are both good:

• the wipers are not needed
• the wipers are not necessary

Polish potrzebny / potrzebna / potrzebne can cover both ideas depending on context.

Not naturally in this sentence.

Polish often drops subject pronouns like ja, ty, oni, because the verb ending already shows the person. But here the subject is a noun:

• szyba
• wycieraczki

If you removed them, the sentence would lose essential information:

• Gdy jest sucha... = When it is dry...
• ...nie są potrzebne. = ...are not needed.

That would only work if the context already made it completely obvious what it and they refer to. On its own, the full sentence with the nouns is the normal form.