Η αποπαρασίτωση γίνεται σήμερα.

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

It matches αποπαρασίτωση, which is a feminine singular noun. Greek articles change for gender, number, and case, so you cannot use just one word for the in every situation.

Here:

• η = the for a feminine singular noun in the nominative case

In Greek, every noun has a grammatical gender: masculine, feminine, or neuter.
Αποπαρασίτωση happens to be feminine, which is why it takes η.

This gender is grammatical, not necessarily logical. English speakers often want to ask why, but in many cases the answer is simply that this is the noun’s lexical gender and you learn it together with the word:

• η αποπαρασίτωση

A good habit is to memorize Greek nouns with their article.

Αποπαρασίτωση is a noun meaning something like deparasitation, deworming, parasite treatment, or pest/parasite removal, depending on context.

It is a fairly formal/technical word, and you may see it in:

• veterinary contexts
• medical contexts
• sanitation/public health contexts
• official instructions or schedules

So even if the general meaning has already been given to you, it is useful to know that this is not usually a very casual everyday noun.

Γίνεται comes from γίνομαι, which often means:

• to happen
• to take place
• to become
• in some contexts, to be done

In this sentence, Η αποπαρασίτωση γίνεται σήμερα, the sense is:

• The treatment is done today
• The deworming takes place today

Greek very often uses γίνεται for events, procedures, appointments, and scheduled actions. Using είναι here would not express the same idea.

So:

• είναι = is
• γίνεται = happens / takes place / is carried out

It is best understood as a middle/passive-form verb from γίνομαι, but in this sentence it functions in a way that often feels passive or impersonal in English.

English says:

• The treatment is done today

Greek often says:

• Η αποπαρασίτωση γίνεται σήμερα

So even though the Greek structure is not a direct copy of the English passive, the effect is similar: the focus is on the event/procedure, not on who does it.

Because Greek, like English, does not always need to mention the agent when it is:

• obvious
• unknown
• unimportant
• not the main focus

Here the important information is simply what is happening and when:

• the deworming/treatment
• today

If needed, Greek can add the person responsible:

• Η αποπαρασίτωση γίνεται σήμερα από τον κτηνίατρο.
  The deworming is done today by the vet.

But very often that extra information is left out.

Γίνεται is present tense, third person singular.

That matches the subject:

• η αποπαρασίτωση = singular

The present tense works here because Greek often uses the present for:

• something happening now
• something taking place today
• a scheduled event

So this can sound like:

• is happening today
• is being done today
• takes place today

This is very natural Greek.

Σήμερα means today, and Greek word order is fairly flexible.

Putting σήμερα at the end is very natural and neutral:

• Η αποπαρασίτωση γίνεται σήμερα.

But you could also say:

• Σήμερα γίνεται η αποπαρασίτωση.

Both are correct, but the emphasis changes slightly.

Very roughly:

• Η αποπαρασίτωση γίνεται σήμερα. = neutral statement; focus may naturally fall on today
• Σήμερα γίνεται η αποπαρασίτωση. = stronger emphasis on today

So the word order is not random; it can help shape emphasis.

Yes, Greek allows more word-order flexibility than English.

For example, all of these are possible:

• Η αποπαρασίτωση γίνεται σήμερα.
• Σήμερα γίνεται η αποπαρασίτωση.
• Γίνεται σήμερα η αποπαρασίτωση.

They all mean roughly the same thing, but the rhythm and emphasis differ.

For learners, the original version is a very safe and natural choice.

A rough pronunciation is:

YEE-neh-tai

More precisely in Modern Greek:

• γι sounds like a soft y sound at the start
• stress is on -νε-

So:

• γίνεται → YEE-ne-te

If you know IPA, it is approximately [ˈʝinete].

A useful thing to notice: the accent mark tells you where the stress goes:

• γίνομαι
• γίνεται

A rough pronunciation is:

a-po-pa-ra-SEE-to-see

The stress falls on σί:

• α-πο-πα-ρα-σί-τω-ση

In IPA, approximately:

• [apoparaˈsitosi]

This is a long word, so learners often find it easier to break it into chunks:

• απο-
• παρασίτ-
• -ωση

Here it is in the nominative singular, because it is the grammatical subject of the sentence:

• Η αποπαρασίτωση γίνεται σήμερα.

You can tell from:

• the article η
• the role of the noun as the thing that happens / takes place

So even though English says The treatment is done today, Greek structures it with the treatment as the subject of γίνεται.

Yes, it sounds natural, especially in a context such as:

• veterinary care
• medical treatment
• building or facility maintenance
• official scheduling

It has a slightly formal/informational tone because of the noun αποπαρασίτωση, but the sentence itself is completely normal Greek.