Klamka do drzwi jest zimna, bo na zewnątrz jest zimno.

Do has several meanings in Polish. Here it does not mean movement to somewhere. After a noun, do + genitive can mean for, meant for, or used with.

So klamka do drzwi is literally something like a handle for a door, which corresponds to English door handle.

A useful comparison:

• klamka do drzwi = a door handle, a handle meant for doors
• klamka od drzwi = the handle of the door / the door’s handle

Both are possible in Polish, but the version with do fits the sentence you were given.

After do, Polish normally uses the genitive case.

So in klamka do drzwi, the noun drzwi is in the genitive. The confusing part is that drzwi often has the same visible form in more than one case, so you do not see an obvious ending change here.

Yes. Drzwi is a plural-only noun in Polish. This type of noun is called pluralia tantum.

So even when English says door in the singular, Polish uses drzwi, which is grammatically plural:

• te drzwi = this door / these doors
• otworzyć drzwi = to open the door

This is just something you have to learn as part of the noun.

Because klamka is a feminine singular noun, and the adjective has to agree with it.

The adjective cold changes like this:

• zimny = masculine
• zimna = feminine
• zimne = neuter

So:

• Klamka jest zimna = The handle is cold

The ending -a matches the feminine noun klamka.

Because jest zimno is an impersonal expression meaning it is cold.

That is different from:

• Klamka jest zimna — here zimna is an adjective agreeing with klamka

In:

• Na zewnątrz jest zimno

there is no noun for zimno to agree with. It expresses a general condition or state: outside, it is cold.

So:

• zimna = adjective agreeing with a feminine noun
• zimno = impersonal it is cold

English needs a dummy subject in weather expressions:

• It is cold
• It is raining

Polish usually does not. It simply says:

• Jest zimno = It is cold
• Pada = It is raining

So jest zimno is a complete sentence even without a word for it.

In normal standard Polish, you keep jest in both parts:

• Klamka do drzwi jest zimna
• na zewnątrz jest zimno

You generally should not leave it out in everyday speech. The repetition may feel heavy to an English speaker, but it is perfectly normal in Polish.

Na zewnątrz means outside or outdoors.

It is a common fixed expression. Another very common everyday alternative is:

• na dworze = outside

So these are both natural:

• Na zewnątrz jest zimno
• Na dworze jest zimno

Yes. Bo means because and is very common in everyday spoken and written Polish.

You could also use ponieważ, which sounds a bit more formal.

Compare:

• Klamka do drzwi jest zimna, bo na zewnątrz jest zimno. — neutral, conversational
• Klamka do drzwi jest zimna, ponieważ na zewnątrz jest zimno. — also correct, slightly more formal

Because Polish normally puts a comma before a clause introduced by bo.

So this punctuation is standard:

• Klamka do drzwi jest zimna, bo na zewnątrz jest zimno.

This is one of those places where Polish comma use is more regular than English learners often expect.

Yes, Polish word order is fairly flexible, but the given sentence is the most neutral version.

Neutral:

• Klamka do drzwi jest zimna, bo na zewnątrz jest zimno.

Possible alternative:

• Bo na zewnątrz jest zimno, klamka do drzwi jest zimna.

That version emphasizes the reason first. So the word order can change, but the original is the most straightforward everyday wording.

A rough English approximation is dzhvee.

More exactly:

• drz sounds somewhat like the j sound in judge, but with Polish pronunciation
• Polish w sounds like English v
• i sounds like ee

So drzwi is approximately dzhvee.

Because Polish has no articles like English a, an, and the.

So klamka can mean:

• a handle
• the handle

The listener understands which one is meant from the context.