Η επιταγή είναι έτοιμη.

Η is the feminine singular form of the definite article, so here it means the.

Greek articles change according to gender, number, and case. In this sentence:

• η = feminine, singular, nominative
• it goes with επιταγή

So η επιταγή is the check/cheque.

Because Greek nouns have grammatical gender. Επιταγή is a feminine noun, and that is simply part of how the word is classified in Greek.

This does not necessarily mean the thing itself is biologically feminine. It just means the noun belongs to the feminine grammatical pattern.

You can often guess gender from the ending, and nouns ending in -ή are very often feminine, though not always.

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

Since επιταγή is:

• feminine
• singular
• nominative

the adjective must also be:

• feminine
• singular
• nominative

So:

• έτοιμος = masculine
• έτοιμη = feminine
• έτοιμο = neuter

That is why έτοιμη is the correct form here.

Είναι is the verb is.

It is the 3rd person singular form of είμαι (to be).
So the structure is:

• Η επιταγή = the subject
• είναι = is
• έτοιμη = ready

Greek normally uses the verb to be in sentences like this, just as English does.

Because Greek does not need a dummy subject like English often does.

In English, you might say It is ready, but in Greek you can simply say:

• Είναι έτοιμη = It is ready / She is ready / It’s ready, depending on context

In your sentence, the subject is stated explicitly:

• Η επιταγή είναι έτοιμη

So there is no need for a separate word meaning it.

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

You can see that from the article too:

• η is the feminine singular nominative article

Also, έτοιμη is in the nominative as well, because it is a predicate adjective referring back to the subject.

A rough pronunciation is:

ee e-pee-ta-YEE EE-ne ET-ee-mee

A slightly more accurate breakdown:

• Η = ee
• επιταγή = e-pee-ta-YEE
• είναι = EE-ne
• έτοιμη = ET-ee-mee

Notes:

• the stress is on -γή in επιταγή
• the stress is on the first syllable of είναι
• the stress is on the first syllable of έτοιμη

Greek uses accent marks to show which syllable is stressed.

In this sentence:

• επιταγή has stress on the last syllable
• είναι has stress on the first syllable
• έτοιμη has stress on the first syllable

But η is a monosyllabic article, and articles like this normally do not take an accent mark.

So the lack of an accent on Η is normal.

Yes. Greek word order is more flexible than English word order.

The most neutral order here is:

• Η επιταγή είναι έτοιμη.

But other orders are possible for emphasis, for example:

• Έτοιμη είναι η επιταγή. = emphasis on ready
• Η επιταγή έτοιμη είναι. = possible, but more marked or stylistic

So the original sentence is the most standard, neutral way to say it.

Normally, no—not in standard everyday Greek for this meaning.

Greek uses the definite article much more often than English does. If you are talking about a specific check/cheque, η is the natural choice:

• Η επιταγή είναι έτοιμη.

Without the article, the sentence sounds unnatural in ordinary usage.

If you wanted an indefinite meaning, you would normally use:

• Μια επιταγή είναι έτοιμη. = A check is ready

Not always. Επιταγή can also mean something like an order, command, or injunction in other contexts.

However, in a sentence like:

• Η επιταγή είναι έτοιμη

the most natural interpretation is usually a bank check/cheque that has been prepared.

So the exact meaning depends on context, but this sentence strongly suggests the banking meaning.

Good question: είναι can be used for both he/she/it is and they are.

So:

• Η επιταγή είναι έτοιμη = singular, because the subject is singular
• Οι επιταγές είναι έτοιμες = plural, because the subject is plural

The form είναι stays the same, and the subject tells you whether it is singular or plural.

Usually, in spoken Greek, you can make it a yes/no question just by using question intonation:

• Η επιταγή είναι έτοιμη;

The word order often stays the same.
You could also say:

• Είναι έτοιμη η επιταγή;

That version can sound a little more clearly question-like, especially in speech.