Η ηλεκτρονική τραπεζική είναι χρήσιμη.

Η is the feminine singular definite article, equivalent to the.

In Η ηλεκτρονική τραπεζική είναι χρήσιμη, the noun phrase η ηλεκτρονική τραπεζική is feminine singular, so the article must also be feminine singular.

Greek definite articles are:

• ο = masculine singular
• η = feminine singular
• το = neuter singular

So here η matches τραπεζική, which is feminine.

In η ηλεκτρονική τραπεζική:

• τραπεζική is the noun
• ηλεκτρονική is the adjective describing it

So literally, the phrase is something like the electronic banking.

A useful thing to notice is that Greek adjectives usually agree with the noun they describe in:

• gender
• number
• case

That is why both words here have feminine singular forms.

Because they are both in the feminine singular nominative form.

• ηλεκτρονική = electronic (feminine singular)
• τραπεζική = banking / bank-related activity (feminine singular noun here)
• χρήσιμη = useful (also feminine singular, because it describes the same subject)

Greek often shows grammatical relationships through word endings, so these matching feminine endings are important.

Here τραπεζική means banking.

It comes from τράπεζα = bank.
The adjective τραπεζικός / τραπεζική / τραπεζικό normally means bank-related or banking, but in some contexts the feminine form τραπεζική can function like a noun and mean banking as an activity or field.

So η ηλεκτρονική τραπεζική is the standard Greek expression for electronic banking or online banking.

Because it matches the subject η ηλεκτρονική τραπεζική, which is feminine singular.

Greek predicate adjectives also agree with the noun they describe. So:

• η τραπεζική είναι χρήσιμη = banking is useful
• το σύστημα είναι χρήσιμο = the system is useful
• ο τρόπος είναι χρήσιμος = the method is useful

So χρήσιμη is the feminine singular form of useful.

είναι means is (or are, depending on context). It is the 3rd person form of the verb to be.

Examples:

• είναι χρήσιμη = is useful
• είναι καλό = is good
• είναι μεγάλα = are big

Unlike English, the same form είναι can mean both is and are. You understand the number from the subject.

The normal, neutral order here is:

Η ηλεκτρονική τραπεζική είναι χρήσιμη.

That is the most natural way to say Electronic banking is useful.

Greek word order is somewhat flexible, though. You might also see:

• Χρήσιμη είναι η ηλεκτρονική τραπεζική.

That version gives more emphasis to χρήσιμη (useful).
But for learners, the original order is the safest and most natural.

A rough pronunciation guide is:

ee ee-lek-tro-nee-KEE tra-peh-ZEE-kee EE-ne hree-see-mee

A few notes:

• η is pronounced like ee
• ηλεκτρονική has stress on the last syllable: -κή
• τραπεζική also has stress on the last syllable: -κή
• είναι is usually pronounced roughly EE-ne
• χρ at the beginning of χρήσιμη may be tricky for English speakers; χ is not an English h, but a rough sound, somewhat like the ch in German Bach or Scottish loch

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

In this sentence:

• ηλεκτρονική → stress on κή
• τραπεζική → stress on κή
• είναι → stress on εί
• χρήσιμη → stress on χρή

Stress matters in Greek pronunciation, so the accent marks are important and should be learned with the word.

Grammatically yes, but it means something different:
The banking is electronic or The banking is electronic in a more literal sense.

The original sentence:

• Η ηλεκτρονική τραπεζική είναι χρήσιμη. means
• Electronic banking is useful.

In the original, ηλεκτρονική is part of the noun phrase electronic banking.
In Η τραπεζική είναι ηλεκτρονική, ηλεκτρονική becomes the complement after είναι, so the structure and meaning change.

Yes, η ηλεκτρονική τραπεζική is a real and natural phrase.

But in everyday speech, people may also say:

• το e-banking
• οι ηλεκτρονικές συναλλαγές = electronic transactions
• η online τραπεζική in less formal or mixed-language contexts

Still, η ηλεκτρονική τραπεζική is perfectly correct and standard Greek.

You add δεν before the verb:

• Η ηλεκτρονική τραπεζική δεν είναι χρήσιμη.
• Electronic banking is not useful.

So the pattern is:

• είναι = is
• δεν είναι = is not

In Greek, a yes/no question often has the same word order as a statement. The difference is mainly in intonation when speaking, or a question mark in writing.

So:

• Η ηλεκτρονική τραπεζική είναι χρήσιμη; means
• Is electronic banking useful?

One important detail: the Greek question mark looks like a semicolon in English.

So in Greek writing:

• ; = question mark

Usually, η should stay.
Greek often uses the definite article in places where English does not.

So the natural sentence is:

• Η ηλεκτρονική τραπεζική είναι χρήσιμη.

Leaving out the article can sound unnatural or incomplete in standard Greek, especially with this kind of abstract noun phrase.

The sentence follows a very common pattern:

[Subject] + [είναι] + [adjective]

So here:

• Η ηλεκτρονική τραπεζική = subject
• είναι = is
• χρήσιμη = useful

This same pattern appears in many Greek sentences:

• Το βιβλίο είναι καλό. = The book is good.
• Η ιδέα είναι ενδιαφέρουσα. = The idea is interesting.
• Το μάθημα είναι εύκολο. = The lesson is easy.

So this is a very useful sentence model to learn.