Βάλε ένα κόμμα εδώ, γιατί χωρίς αυτό η πρόταση ακούγεται περίεργη.

Βάλε is the singular informal imperative of βάζω (to put).

So it is what you say when telling one person directly to do something:

• Βάλε ένα κόμμα. = Put a comma.
• Βάλτε ένα κόμμα. = Put a comma. (plural or polite singular)

More specifically, βάλε is the aorist imperative, which is very common for a simple instruction: do this action.

Greek often uses two imperative types:

• βάλε = aorist imperative
• βάζε = present imperative

In a sentence like this, βάλε sounds natural because it means do this one action: put a comma here.

By contrast, βάζε usually suggests something repeated, ongoing, or habitual, like keep putting or put regularly, which does not fit as well here.

Ένα is the neuter form of one / a.

Since κόμμα is a neuter singular noun, the article/number must match it:

• ένα κόμμα = a comma / one comma

Greek often uses ένας / μία or μια / ένα in places where English uses a/an.

Also, κόμμα is neuter, so ένα is the correct form.

Κόμμα is neuter.

That matters because words that go with it must match its gender, number, and case when relevant. For example:

• ένα κόμμα = a comma
• αυτό = it / this, referring back to κόμμα

The pronoun αυτό is also neuter here because it refers to κόμμα.

No. Κόμμα can also mean political party.

So Greek learners often meet both meanings:

• ένα κόμμα = a comma
• ένα πολιτικό κόμμα = a political party

In this sentence, the context clearly shows it means comma.

Greek word order is more flexible than English word order.
So Βάλε ένα κόμμα εδώ is natural and means Put a comma here.

You could also hear variations such as:

• Βάλε εδώ ένα κόμμα
• Εδώ βάλε ένα κόμμα

These can shift emphasis slightly, but the basic meaning stays the same.
The version in your sentence sounds very normal.

In Greek, a comma before γιατί is very common when γιατί introduces the reason for what comes before:

• Βάλε ένα κόμμα εδώ, γιατί...

This works much like English:

• Put a comma here, because...

So the comma separates the main instruction from the explanatory reason.

Here γιατί means because and introduces a reason:

• Βάλε ένα κόμμα εδώ, γιατί...
• Put a comma here, because...

Greek γιατί can also mean why in questions:

• Γιατί έφυγες; = Why did you leave?

So learners often need to rely on context:

• in a statement: often because
• in a question: often why

Χωρίς normally takes the accusative, so αυτό is in the accusative here.

• χωρίς αυτό = without it

Because αυτό refers to κόμμα, and κόμμα is neuter singular, the form is αυτό.

Useful comparison:

• χωρίς αυτόν = without him
• χωρίς αυτή = without her
• χωρίς αυτό = without it

Greek often uses a pronoun where English would use it:

• χωρίς αυτό = without it

This avoids repetition and sounds natural.
You could repeat the noun and say χωρίς το κόμμα, but χωρίς αυτό is smoother here because the comma was just mentioned.

Because η πρόταση is the subject of ακούγεται.

In other words, it is the sentence that sounds strange.

• η πρόταση = the sentence
• ακούγεται = sounds
• περίεργη = strange

So nominative is used because η πρόταση is the thing doing the sounding.

Ακούγεται is the mediopassive form of ακούω.

In Greek, this form is often used for meanings like:

• is heard
• sounds

So:

• Η πρόταση ακούγεται περίεργη. = The sentence sounds strange.

This is a very common Greek structure.
English says sounds strange, while Greek literally uses a form closer to is heard as strange, though in normal usage it simply means sounds strange.

Because it agrees with η πρόταση, which is a feminine singular noun.

Greek adjectives must agree with the noun they describe in gender, number, and case:

• η πρόταση = feminine singular
• περίεργη = feminine singular

Compare:

• ο ήχος ακούγεται περίεργος = the sound sounds strange
• η πρόταση ακούγεται περίεργη = the sentence sounds strange
• το κείμενο ακούγεται περίεργο = the text sounds strange

Yes. Περίεργος / περίεργη / περίεργο can mean:

• strange
• odd
• weird
• sometimes even curious depending on context

In this sentence, strange or odd is the best fit: the sentence sounds odd without the comma.

It is informal because of Βάλε, which is the singular informal imperative.

If you wanted to make it polite or address more than one person, you would say:

• Βάλτε ένα κόμμα εδώ, γιατί χωρίς αυτό η πρόταση ακούγεται περίεργη.

So the original sentence sounds like you are talking to one person in a normal, everyday way.

In some contexts, Greek can omit articles, but here η πρόταση sounds the most natural.

Greek uses the definite article more often than English does, especially when referring to something specific and understood in context. Here it means the sentence, not just a sentence.

So:

• η πρόταση = the sentence

is the expected choice.

No, Greek word order is fairly flexible, though some versions sound more natural than others.

The original sentence:

• Βάλε ένα κόμμα εδώ, γιατί χωρίς αυτό η πρόταση ακούγεται περίεργη.

is natural and neutral.

You might also hear:

• Βάλε εδώ ένα κόμμα, γιατί χωρίς αυτό η πρόταση ακούγεται περίεργη.
• Γιατί χωρίς αυτό η πρόταση ακούγεται περίεργη, βάλε ένα κόμμα εδώ.

These alternatives shift emphasis, but the original is probably the most straightforward everyday version.