Η ραπτομηχανή λειτουργεί καλά.

Η is the definite article meaning the for a feminine singular noun in the nominative case.

So:

• η = the (feminine singular, nominative)
• ραπτομηχανή is a feminine noun
• together: η ραπτομηχανή = the sewing machine

Greek articles change depending on gender, number, and case, so you cannot use just one word for the in every situation the way you do in English.

One clue is the article: η tells you the noun is feminine.

Also, many feminine Greek nouns end in -ή, and ραπτομηχανή is one of them.

So in this sentence:

• η ραπτομηχανή = feminine singular subject

You should not assume every noun ending in -ή is feminine, but it is a very common pattern.

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

The subject is the thing doing the action or being described. Here, the sewing machine is the thing that functions/works well.

So:

• Η ραπτομηχανή = the subject
• therefore it is in the nominative

λειτουργεί means it works, it functions, or it operates.

In this sentence, it describes how the sewing machine is functioning:

• Η ραπτομηχανή λειτουργεί καλά.
• The sewing machine works well.

This verb is often used for:

• machines
• devices
• systems
• businesses or services
• sometimes even body parts or plans

So it is broader than just mechanical work in English; it often means to function properly.

It is the 3rd person singular present tense form.

That means it corresponds to:

• he/she/it works
• he/she/it functions

Since ραπτομηχανή is a singular noun, the verb is singular too.

You can think of it as:

• εγώ λειτουργώ = I function / I operate
• εσύ λειτουργείς = you function
• αυτό/αυτή/αυτό λειτουργεί = it/he/she functions

Here the subject is a thing, so in English we translate it as it works.

Greek always marks the stressed syllable in normal writing, and in λειτουργεί the stress falls on the last syllable: -γεί.

So you stress it like this:

• λειτουργεί

This is just part of the correct written form and pronunciation of the word.

Because καλά is being used as an adverb, not as an adjective.

Compare:

• καλός / καλή / καλό = good
  These are adjectives and must agree with a noun.
• καλά = well
  This is an adverb and describes how something works.

So:

• Η ραπτομηχανή είναι καλή. = The sewing machine is good.
• Η ραπτομηχανή λειτουργεί καλά. = The sewing machine works well.

That is the key difference:

• adjective = describes a noun
• adverb = describes a verb

In everyday modern Greek, καλά is the normal and natural choice here.

Although καλώς exists, it is much less common in ordinary speech for this kind of sentence and can sound formal, fixed, or old-fashioned depending on context.

So for a learner, the safest and most useful version is:

• λειτουργεί καλά

The neutral, natural order is:

• Η ραπτομηχανή λειτουργεί καλά.

Greek word order is more flexible than English, because endings and articles give a lot of grammatical information. So other orders are sometimes possible for emphasis, but they may sound marked or less neutral.

For example, moving καλά earlier could add emphasis to well.

If you are learning, the best default pattern is:

• subject + verb + adverb

Normally, no, not in an ordinary sentence like this.

Greek uses the definite article very often, much more than English does. If you mean the sewing machine, the normal form is:

• Η ραπτομηχανή λειτουργεί καλά.

Leaving out the article might sound unnatural, incomplete, or like a headline, label, or note rather than a normal sentence.

No. In modern Greek, η is pronounced like ee.

So Η here sounds like:

• ee

It is not pronounced like English he, and it does not have an h sound in modern standard Greek.

A rough English-style approximation is:

• ee rap-to-mi-ha-NEE lee-tour-YEE ka-LA

A few notes:

• ραπτομηχανή has stress on the last syllable: -νή
• λειτουργεί has stress on the last syllable: -γεί
• καλά has stress on the last syllable: -λά

A more careful approximation would be something like:

• ee rapto-meecha-NEE leetour-YEE ka-LA

But the exact sounds are a bit different from English, especially χ and γ before front vowels.

Yes. It is a compound noun.

It is built from elements related to:

• ραπτο- = sewing
• μηχανή = machine

So ραπτομηχανή literally means sewing machine.

Greek forms many compound words this way, and learning to recognize parts like this can help you guess meanings of new vocabulary.