Το ποσοστό επιχορήγησης είναι υψηλό.

Το is the definite article meaning the.

It is in the neuter singular nominative form because it goes with ποσοστό, which is a neuter singular noun.

So:

• το = the for a neuter singular noun
• ποσοστό = percentage / rate

Together, το ποσοστό means the percentage or the rate.

Ποσοστό usually means percentage, rate, or proportion, depending on context.

In this sentence, it refers to the rate/percentage of funding or subsidy.

So το ποσοστό επιχορήγησης is literally something like:

• the percentage of subsidy
• the grant rate
• the funding percentage

The most natural English translation depends on the wider context.

Because it is in the genitive case.

The basic form is:

• η επιχορήγηση = the grant / subsidy / funding

But after another noun, Greek often uses the genitive to mean of ...

So:

• ποσοστό επιχορήγησης = percentage of grant/subsidy
• literally: percentage of funding

This is a very common Greek structure:

• το κέντρο της πόλης = the center of the city
• η τιμή του προϊόντος = the price of the product
• το ποσοστό επιχορήγησης = the rate of subsidy

So επιχορήγησης is the genitive singular form of επιχορήγηση.

Είναι means is (or are, depending on the subject).

It is the 3rd person singular/plural form of the verb είμαι = to be.

Here the subject is singular:

• Το ποσοστό επιχορήγησης = The grant rate
• είναι = is
• υψηλό = high

So the whole sentence means The grant rate is high.

Because υψηλό has to agree with ποσοστό, which is neuter singular.

Greek adjectives change form to match the noun in gender, number, and case.

Here are the basic singular forms of high:

• υψηλός = masculine
• υψηλή = feminine
• υψηλό = neuter

Since ποσοστό is neuter singular, the adjective must also be neuter singular:

• Το ποσοστό είναι υψηλό.

Even though υψηλό comes after είναι, it still agrees with the subject. This is called a predicate adjective.

Because υψηλό is not being used as a separate noun phrase like the high one. It is simply describing the subject after the verb to be.

Compare:

• Το ποσοστό είναι υψηλό. = The rate is high.
• Το υψηλό ποσοστό = the high rate

In the sentence you gave, υψηλό is a predicate adjective, so it normally appears without an article.

Yes, Greek word order is more flexible than English.

The neutral order is:

• Το ποσοστό επιχορήγησης είναι υψηλό.

But you may also see:

• Υψηλό είναι το ποσοστό επιχορήγησης.
• Είναι υψηλό το ποσοστό επιχορήγησης.

These alternatives can shift the focus or emphasis, but the basic meaning stays the same.

For learners, the original version is the most straightforward and natural neutral order: subject + verb + adjective.

A simple pronunciation guide is:

• Το ≈ toh
• ποσοστό ≈ po-so-STO
• επιχορήγησης ≈ e-pee-ho-REE-yee-sees
• είναι ≈ EE-ne
• υψηλό ≈ eep-see-LO

A more connected approximation:

to po-so-STO e-pee-ho-REE-yee-sees EE-ne eep-see-LO

A couple of useful points:

• Greek stress is marked by the accent mark: ποσοστό, επιχορήγησης, υψηλό
• αι in είναι is pronounced like e
• η, ι, υ often sound like ee in Modern Greek

Yes. Υψηλό is very natural for things like:

• percentages
• rates
• prices
• levels
• amounts

Examples:

• υψηλό ποσοστό = high percentage
• υψηλή τιμή = high price
• υψηλό επίπεδο = high level

Its opposite is:

• χαμηλό = low (neuter singular)

So you could also say:

• Το ποσοστό επιχορήγησης είναι χαμηλό. = The grant rate is low.

The dictionary forms are:

• το = the (neuter singular article)
• ποσοστό = percentage / rate
• η επιχορήγηση = grant / subsidy / funding
• είμαι = to be
• υψηλός, υψηλή, υψηλό = high

This is useful because in Greek, words often appear in changed forms inside sentences, especially:

• nouns in different cases, like επιχορήγησης
• adjectives that change for gender, like υψηλό