Αυτό το μοντέλο λειτουργεί καλά.

Yes, together they express this, but Greek commonly uses both the demonstrative and the article:

• αυτό = this
• το = the

So Αυτό το μοντέλο literally looks like this the model, but that is the normal Greek pattern.

This is very common in Greek:

• αυτό το βιβλίο = this book
• αυτή η πόρτα = this door
• αυτό το σπίτι = this house

So even though it feels redundant to an English speaker, it is standard Greek.

Because μοντέλο is a neuter noun, and the demonstrative has to agree with it in gender, number, and case.

Here are the singular forms of this in the nominative:

• αυτός = masculine
• αυτή = feminine
• αυτό = neuter

Since το μοντέλο is neuter, Greek uses:

• αυτό το μοντέλο = this model

Agreement is very important in Greek.

It is a borrowed word, but in Greek it is treated as a neuter noun. Many nouns ending in -ο are neuter, and το μοντέλο follows that pattern.

So:

• το μοντέλο = the model
• ένα μοντέλο = a model
• αυτό το μοντέλο = this model

Even when a noun is borrowed from another language, Greek still assigns it a grammatical gender.

λειτουργεί comes from the verb λειτουργώ and means something like:

• works
• functions
• operates

In this sentence, it means that the model performs well or functions properly:

• Αυτό το μοντέλο λειτουργεί καλά. = This model works well.

Depending on context, λειτουργεί can be used for machines, systems, plans, methods, and even abstract things like ideas or arrangements.

Because this is the third person singular present form of λειτουργώ.

The subject is Αυτό το μοντέλο = this model, which is it in English. So the verb must mean it works / it functions.

A few forms of λειτουργώ:

• λειτουργώ = I work / function
• λειτουργείς = you work / function
• λειτουργεί = he/she/it works / functions
• λειτουργούμε = we work / function
• λειτουργείτε = you all work / function
• λειτουργούν or λειτουργούνε = they work / function

So λειτουργεί is used because the subject is singular.

Because καλά is an adverb, not an adjective.

In the sentence, it describes how the model functions:

• λειτουργεί καλά = works well

Compare:

• καλός / καλή / καλό = good (adjective, describes a noun)
• καλά = well (adverb, describes a verb)

So:

• ένα καλό μοντέλο = a good model
• το μοντέλο λειτουργεί καλά = the model works well

That distinction is the same as good vs well in English.

Yes. That would mean:

• Το μοντέλο λειτουργεί καλά. = The model works well.

Adding Αυτό makes it specifically this model, often with a contrastive or pointing sense:

• Αυτό το μοντέλο λειτουργεί καλά. = This model works well.

So the version with αυτό is more specific.

Possibly, yes. μοντέλο can mean different things depending on context, such as:

• model
• design
• version
• pattern
• prototype
• fashion model, in other contexts

So the exact English translation depends on what kind of model is being discussed. But grammatically, the Greek sentence stays the same.

The basic order here is:

• Αυτό το μοντέλο = subject
• λειτουργεί = verb
• καλά = adverb

So it follows a straightforward Subject + Verb + Adverb pattern:

• Αυτό το μοντέλο λειτουργεί καλά.

Greek word order is more flexible than English, so other orders are possible for emphasis, for example:

• Καλά λειτουργεί αυτό το μοντέλο.
• Αυτό το μοντέλο καλά λειτουργεί.

But the original sentence is the most neutral and natural for most situations.

Just because it starts the sentence.

Normally, inside a sentence, it would be written lowercase:

• Νομίζω ότι αυτό το μοντέλο λειτουργεί καλά. = I think that this model works well.

So the capital Α in Αυτό is only sentence-initial capitalization.

A helpful approximation is:

af-TO to mon-DE-lo lee-tour-GHI ka-LA

A few pronunciation notes:

• αυτό has the stress on the second syllable: αυ-ΤΟ
• μοντέλο has the stress on -ντέ-
• λειτουργεί has the stress on the final -εί
• καλά has the stress on the last syllable

The written accent marks in Greek show you where the stress falls, which is very useful for learners.

It is in the nominative singular, because it is the subject of the sentence.

You can tell from:

• το μοντέλο = the model
• αυτό το μοντέλο = this model

Since this is the thing doing the action of λειτουργεί, it is the subject, so the nominative is expected.

Usually it is used more naturally for things like:

• machines
• systems
• methods
• plans
• software
• devices
• arrangements

For a person, Greek would usually choose a different verb depending on the meaning. For example, if you mean someone is doing well, functioning well, or performing well, other expressions may sound more natural.

So in this sentence, the combination μοντέλο λειτουργεί καλά strongly suggests a non-human thing or system functioning effectively.