Η επιφάνεια είναι καθαρή.

Word by word:

• Η = the (feminine singular)
• επιφάνεια = surface
• είναι = is
• καθαρή = clean (feminine singular form)

So the structure is literally:

• The surface is clean.

Η is the definite article meaning the.

It is used because επιφάνεια is a feminine singular noun in the nominative case. Greek articles change according to gender, number, and case.

Here are the nominative singular definite articles:

• ο = the (masculine)
• η = the (feminine)
• το = the (neuter)

Since επιφάνεια is feminine, it takes η.

In this sentence, Η is pronounced ee, like the ee in see.

So:

• Η = /i/

A learner should also know that uppercase Η here is just the capital form of the article η because it is at the beginning of the sentence.

είναι is the present-tense form of the verb είμαι = to be.

In this sentence, it means is:

• Η επιφάνεια είναι καθαρή. = The surface is clean.

A useful thing to know: είναι is also used for they are in Modern Greek.

Examples:

• Η επιφάνεια είναι καθαρή. = The surface is clean.
• Οι επιφάνειες είναι καθαρές. = The surfaces are clean.

So Greek uses the same form είναι for both is and are in some contexts.

Because adjectives in Greek must agree with the noun they describe.

Since επιφάνεια is:

• feminine
• singular
• nominative

the adjective must also be:

• feminine
• singular
• nominative

So we get:

• masculine: καθαρός
• feminine: καθαρή
• neuter: καθαρό

Compare:

• Ο χώρος είναι καθαρός. = The room/space is clean.
• Η επιφάνεια είναι καθαρή. = The surface is clean.
• Το τραπέζι είναι καθαρό. = The table is clean.

Because καθαρή is a predicate adjective, not a noun phrase.

In Η επιφάνεια είναι καθαρή, the pattern is:

• subject: Η επιφάνεια
• verb: είναι
• predicate adjective: καθαρή

This works like English The surface is clean, where clean also does not take the.

If you put an article before the adjective, it would change the structure and meaning.

The sentence as given has a very normal, neutral word order:

• Η επιφάνεια είναι καθαρή.

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

• Καθαρή είναι η επιφάνεια.

This can sound more contrastive or emphatic, something like:

• It’s the surface that is clean
• or The surface is clean

But the version you were given is the most straightforward and natural basic order for learners.

A rough pronunciation is:

• ee e-pee-FA-nya EE-ne ka-tha-REE

A more IPA-like version is:

• [i epiˈfaɲa ˈine kaθaˈri]

A few details:

• επιφάνεια has the stress on φά
• είναι has the stress on εί
• καθαρή has the stress on the last syllable, ρή
• θ in καθαρή is like English th in think, not in this

Greek uses an accent mark to show which syllable is stressed.

In this sentence:

• επιφάνεια → stress on φά
• είναι → stress on εί
• καθαρή → stress on ρή

Stress matters in Greek pronunciation, so learners should pay attention to it from the start.

It is in the nominative singular.

That is because it is the subject of the sentence:

• The surface is clean.

In Greek, subjects normally appear in the nominative case.

So:

• Η επιφάνεια = nominative singular feminine

In normal standard Modern Greek, no—you usually keep είναι in a sentence like this.

So:

• Η επιφάνεια είναι καθαρή. = correct

Leaving it out would sound incomplete or unnatural in ordinary usage.

Greek is not like some languages where the present tense of to be is often omitted.

Not always.

Its basic meaning is surface, especially a physical surface, which is the most likely meaning here. But depending on context, επιφάνεια can also be used in more specialized ways, such as:

• surface area in mathematics or geometry
• the visible surface of something
• sometimes more technical senses depending on the field

In this sentence, though, the natural understanding is simply a physical surface that is clean.

If you want to say The surfaces are clean, the sentence becomes:

• Οι επιφάνειες είναι καθαρές.

Changes:

• Η → Οι for plural the
• επιφάνεια → επιφάνειες for plural surfaces
• καθαρή → καθαρές so the adjective agrees in the feminine plural
• είναι stays είναι

This is a good example of how Greek articles, nouns, and adjectives all change together.

Yes, that can confuse beginners.

• η / Η without an accent = the feminine article the
• ή / Ή with an accent = or

In your sentence:

• Η επιφάνεια... = The surface...

Because it is the article, there is no accent. The only reason it is capitalized is that it begins the sentence.