Ten zakręt jest ostry, więc trzeba jechać wolniej.

Because zakręt is a masculine singular noun, so the demonstrative this must also be masculine singular: ten.

Polish this changes by gender:

• ten = masculine
• ta = feminine
• to = neuter

So:

• ten zakręt = this turn
• but, for example, ta droga = this road
• to skrzyżowanie = this intersection

Zakręt means a bend, curve, or turn in a road.

It usually refers to the physical shape of the road rather than the act of turning. So in this sentence, it means a sharp bend in the road.

A learner might compare it with:

• skręt = a turn, often the act of turning
• zakręt = a bend/curve in the road itself

Yes. Ostry literally means sharp, and Polish uses it naturally for things like:

• ostry nóż = a sharp knife
• ostry zakręt = a sharp turn

So this is very similar to English. The adjective agrees with zakręt, which is masculine singular, so we get ostry.

Because it has to agree with zakręt in gender, number, and case.

Here:

• zakręt = masculine
• singular
• nominative case

So the adjective also takes the masculine singular nominative form:

• ostry zakręt

If the noun changed, the adjective would change too:

• ostra droga = a sharp road/route bend idea in feminine form
• ostre światło = sharp/harsh light

Jest means is.

In the present tense, Polish sometimes omits jest in informal speech, especially in very simple statements, but in a normal full sentence like this, Ten zakręt jest ostry is the standard and safest form for learners.

So:

• Ten zakręt jest ostry = standard, complete
• Ten zakręt ostry = not the normal neutral form here

Unlike Russian, Polish usually keeps the present-tense to be in sentences like this.

Yes. Więc means so, therefore, or thus.

It connects the two parts of the sentence:

• Ten zakręt jest ostry = This turn is sharp
• więc trzeba jechać wolniej = so one has to drive more slowly

It is a very common way to express a result or consequence.

Trzeba means something like:

• it is necessary
• one must
• you have to
• it is needed

It is an impersonal form. That means there is no specific subject stated.

So trzeba jechać wolniej literally means something like:

• it is necessary to drive more slowly

In natural English, we often translate it as:

• you have to drive more slowly
• one has to drive more slowly

It does not specifically mean I, you, or we unless context tells you that.

Because jechać is used for travelling by vehicle:

• by car
• by bus
• by bike
• by train, etc.

Since the sentence is about a road bend, driving is implied, so jechać fits naturally.

Compare:

• iść = to go on foot, to walk
• jechać = to go by vehicle
• chodzić = to walk/go regularly, or on foot in a repeated/general sense

So:

• trzeba jechać wolniej = one has to drive/go more slowly
• trzeba iść wolniej would mean one has to walk more slowly

Because wolniej is the comparative adverb of wolno.

• wolno = slowly
• wolniej = more slowly

So:

• jechać wolno = to drive slowly
• jechać wolniej = to drive more slowly

In this sentence, the idea is not just slowly, but slower than usual / slower than before / slower because of the sharp bend.

Yes, wolniej is grammatically comparative: more slowly / slower.

The comparison is often implicit, not stated directly. It means something like:

• slower than you are going now
• slower than usual
• slower than on a straight road
• slower than would otherwise be safe

Polish often leaves that comparison unstated when it is obvious from context.

Yes, but the meaning changes slightly.

• trzeba jechać wolniej = one has to / it is necessary to drive more slowly
  This is more general and impersonal.
• musisz jechać wolniej = you must drive more slowly
  This directly addresses one person.

So if you are giving advice or instructions to a specific driver, musisz is possible. But the original sentence sounds more general, like a statement about what is necessary in that situation.

To some extent, yes. Polish word order is more flexible than English, but not completely free.

The given sentence:

• Ten zakręt jest ostry, więc trzeba jechać wolniej.

is the most neutral and natural version.

You might also hear variations for emphasis, but they can sound marked:

• Trzeba jechać wolniej, bo ten zakręt jest ostry.
• Więc trzeba jechać wolniej after the first clause is very natural.

For learners, it is best to keep the original order unless you have a reason to emphasize something.

A rough pronunciation guide is:

• ten ≈ ten
• zakręt ≈ ZA-krent
• jest ≈ yest
• ostry ≈ OS-trih
• więc ≈ vyents
• trzeba ≈ TSHE-ba
• jechać ≈ YE-hach
• wolniej ≈ VOL-nyey

About ę in zakręt: before certain consonants, it is often pronounced more like en/em in actual speech, so zakręt sounds close to zakrent.

That is normal Polish pronunciation, even though the spelling stays ę.

Because Polish often uses impersonal constructions where English prefers a personal subject.

So Polish says:

• trzeba jechać wolniej

instead of explicitly saying:

• ty musisz jechać wolniej

This makes the statement sound more general, objective, and less directly aimed at one person. English often uses you in a general sense, but Polish does not need to do that here.