Κλείσε το φερμουάρ στο μπουφάν σου, γιατί κάνει κρύο.

Κλείσε is the singular, informal imperative of κλείνω (to close / to shut).

So it is used when speaking to one person you address as you in an informal way:

• Κλείσε = close! / shut! / zip up!

If you were speaking to:

• more than one person, or
• one person formally,

you would say Κλείστε.

This imperative is based on the aorist stem, which often gives the idea of a single, complete action: Close it now.

In Greek, κλείνω is the normal verb for closing many things, including:

• doors
• windows
• lights in some contexts? no, not usually
• zippers

So κλείσε το φερμουάρ literally uses the idea close the zipper, but in natural English we often say zip up your jacket.

Greek does not need a special verb equivalent to English zip up here. Using κλείνω sounds completely natural.

Because φερμουάρ is a neuter noun, so it takes the neuter singular article το.

Here, το φερμουάρ is the direct object of Κλείσε:

• Κλείσε = close
• το φερμουάρ = the zipper

Also, φερμουάρ is a loanword and is usually treated as indeclinable, so the noun itself does not change form much. The article often shows the grammar:

• το φερμουάρ = nominative/accusative singular

στο is the contraction of σε + το.

So:

• σε το → στο

In this sentence, στο μπουφάν σου means something like:

• on your jacket
• in your jacket
• on the jacket you’re wearing

With clothing and attached parts like a zipper, Greek often uses σε / στο in this way.

So το φερμουάρ στο μπουφάν σου means the zipper on your jacket.

That is the normal Greek pattern for a possessive pronoun in this kind of phrase:

• το μπουφάν σου = your jacket
• literally: the jacket your

Greek usually places these short possessive forms after the noun:

• μου = my
• σου = your
• του / της = his / her
• μας = our
• σας = your
• τους = their

So the structure is very often:

article + noun + possessive clitic

For example:

• το σπίτι μου = my house
• η τσάντα σου = your bag

After στο (σε + το), the noun is in the accusative.

So grammatically, μπουφάν here is accusative singular. But μπουφάν is another loanword that is usually indeclinable, so its form stays the same.

That means the article does a lot of the grammatical work:

• το μπουφάν = the jacket

This is common with some modern borrowed nouns in Greek.

Because γιατί introduces a reason clause:

• γιατί κάνει κρύο = because it’s cold

So the sentence has:

1. the main command: Κλείσε το φερμουάρ στο μπουφάν σου
2. the explanation: γιατί κάνει κρύο

Greek commonly uses a comma before this kind of explanatory clause, especially in standard writing.

Because κάνει κρύο is the normal Greek expression for the weather is cold or it’s cold.

Literally, κάνει means it makes / it does, but in weather expressions Greek uses κάνει idiomatically:

• κάνει κρύο = it’s cold
• κάνει ζέστη = it’s hot
• κάνει καλό καιρό = the weather is nice

By contrast, είναι κρύο usually describes something as cold:

• Το νερό είναι κρύο = The water is cold

So for general weather, κάνει κρύο is the natural choice.

Greek often leaves subject pronouns out when they are already clear from the verb form.

In this sentence:

• Κλείσε already tells you the subject is you singular, informal
• κάνει can be used without an expressed it in weather expressions

So Greek does not need:

• an explicit you in the command
• a dummy it like English uses in it’s cold

This is very normal Greek grammar.

The word order here is very natural, but Greek word order is more flexible than English.

The sentence as given:

• Κλείσε το φερμουάρ στο μπουφάν σου, γιατί κάνει κρύο.

This is the most straightforward order:

1. command first
2. reason second

Greek could change the order for emphasis, for example:

• Γιατί κάνει κρύο, κλείσε το φερμουάρ στο μπουφάν σου.

That is still grammatical, but it may sound more marked or more deliberately explanatory.

Inside the noun phrase, though, the order το μπουφάν σου is the normal one, not σου το μπουφάν in ordinary neutral speech.

Yes. φερμουάρ is a very common everyday word for zipper / zip.

It is a borrowing, but it is completely normal in modern Greek. A learner should definitely know it.

You may also notice that both φερμουάρ and μπουφάν are everyday clothing words that came into Greek from other languages. Modern Greek uses many such loanwords naturally in daily speech.