Learn Hardcore Greek: Ο φίλος μου γράφει κριτική για μια καινούρια ταινία στο ίντερνετ. - My friend is writing a review of a new movie on the internet.

Ο φίλος μου = my (particular) friend, the one both speaker and listener can identify.
φίλος μου (without article) is possible but less neutral; it can sound more like a fragment, a caption, or focus-y speech (e.g. in lists, titles, or very informal short utterances).
ένας φίλος μου = a friend of mine (one among several friends, not a specific, previously-known one).

So here Ο φίλος μου means “my friend” in the usual, specific sense, so the definite article Ο is used.

Why is μου (my) after φίλος and not before it, like in English?

In Greek, the unstressed possessive pronouns (my, your, his, etc.) normally come after the noun as enclitics:

ο φίλος μου = my friend
η μητέρα σου = your mother
το βιβλίο του = his book

So Greek doesn’t say μου φίλος in standard speech for “my friend”. The pattern is:

article + noun + possessive pronoun
ο φίλος μου, η φίλη μου, το σπίτι μας, κτλ.

There is also a stressed possessive form (e.g. δικός μου φίλος) but that has an emphatic meaning (a friend of mine / my own friend), not the neutral “my friend”.

What exactly does γράφει mean here – “writes” or “is writing”? Why is there only one form?

Γράφει is the 3rd person singular present indicative of γράφω (to write).

Person: he / she / it
Number: singular
Tense: present
Mood: indicative
Voice: active

Greek has only one present form for both:

English simple present: He writes reviews.
English present continuous: He is writing a review.

So (ο φίλος μου) γράφει κριτική can mean:

“My friend writes a review (as a habit)” or
“My friend is writing a review (right now).”

The exact English translation (writes vs. is writing) depends on context, not on a different Greek form.

Why is it κριτική without μια or την? Shouldn’t it be μια κριτική (“a review”)?

Κριτική is a feminine noun in the accusative singular here, functioning as the direct object of γράφει:

(ποιος;) ο φίλος μου – subject
(τι κάνει;) γράφει – verb
(τι γράφει;) κριτική – direct object

In Greek you don’t always need an article with a singular object, especially with:

abstract nouns, or
activities where the noun feels almost like “doing X” (e.g. κάνει γυμναστική, “does exercise”).

γράφει κριτική can mean “he is doing (some) review writing”.
You can say γράφει μια κριτική (“he is writing a review”) if you want to emphasize one specific review as a countable thing. Both are correct; the version without μια feels a bit more general or activity-like.

Why is the preposition για used with κριτική – why not σε or something else?

The common expression in Greek is:

γράφω κριτική για κάτι = I write a review / criticism about something.

Here για means about / concerning:

μιλάω για την ταινία = I talk about the movie
σκέφτομαι για σένα = I think about you
κάνει κριτική για το βιβλίο = he/she critiques the book

Using σε would change the meaning or sound wrong in this context. σε is more literal “in, to, at” (e.g. γράφω σε χαρτί = I write on paper), while για is the standard choice for “about” when it comes to opinions, criticism, discussion, etc.

What is going on grammatically in μια καινούρια ταινία? How do the words agree?

μια καινούρια ταινία consists of:

μια – feminine singular indefinite article, accusative case
καινούρια – feminine singular adjective (new), accusative case
ταινία – feminine singular noun (movie), accusative case

They all agree in:

gender: feminine
number: singular
case: accusative (because they’re the object of the preposition για)

Word order is:

[indefinite article] + [adjective] + [noun]
μια καινούρια ταινία = a new movie

You could also say για μια ταινία (without the adjective) or για την καινούρια ταινία (the new movie – a specific one).

What is στο exactly? Why not σε το or something like that?

στο is a contraction of the preposition σε and the neuter definite article το:

σε + το = στο

So:

σε = in, on, at, to (very general preposition)
το ίντερνετ = the internet
στο ίντερνετ = in/on the internet

Other common contractions:

σε + τον = στον (e.g. στον δρόμο – in the street)
σε + την = στην (e.g. στην πόλη – in the city)
σε + τους = στους
σε + τις = στις

You almost always use these contracted forms in normal speech and writing.

Why is it στο ίντερνετ and not something like στον ίντερνετ?

Because ίντερνετ is treated as a neuter noun in Greek and is indeclinable (it doesn’t change form):

το ίντερνετ (nominative/accusative, same form)
There is no ο ίντερνετ or τον ίντερνετ.

So the correct contraction is:

σε + το ίντερνετ → στο ίντερνετ

If you used the masculine article (στον), you’d be implying it’s a masculine noun, which it isn’t.

Could we say Ο φίλος μου γράφει μια κριτική για μια καινούρια ταινία στο ίντερνετ? Does that change the meaning?

Yes, that is perfectly correct, and it slightly shifts the nuance:

γράφει κριτική – more like “he is doing review-writing” (activity/general).
γράφει μια κριτική – clearly “he is writing a review”, one specific piece of text.

In many contexts, the difference is small and both could be translated “He is writing a review of a new movie on the internet.” Native speakers can use either, depending on how “countable” or “specific” they feel the review is in that moment.

Can I change the word order, for example put στο ίντερνετ earlier in the sentence?

Greek word order is fairly flexible. All of these are grammatically possible, with small differences in emphasis:

Ο φίλος μου γράφει κριτική για μια καινούρια ταινία στο ίντερνετ.
(neutral; the internet location comes as extra info at the end)
Ο φίλος μου στο ίντερνετ γράφει κριτική για μια καινούρια ταινία.
(light emphasis on “online” – it’s online where my friend writes reviews...)
Στο ίντερνετ ο φίλος μου γράφει κριτική για μια καινούρια ταινία.
(stronger focus on “on the internet” – contrast with other places)

What doesn’t change easily is the close link between:

ο φίλος μου (article + noun + possessive together)
μια καινούρια ταινία (article + adjective + noun together)

What is the difference between καινούρια and νέα for “new”?

Both καινούρια and νέα can mean “new”, but there is a nuance:

καινούρια ταινία
- “a new movie” in the sense of fresh, recently made/released, or new to me.
νέα ταινία
- often also “new movie”, but νέος/νέα/νέο can have more of a “recent / young” feeling and is used very widely in many contexts (new generation, news, etc.).

In this sentence, μια καινούρια ταινία is very natural and common for “a new movie (that just came out).”
μια νέα ταινία is also correct, slightly more formal or journalistic in tone.

Is ίντερνετ always written like that in Greek, or are there more “Greek” alternatives?

Το ίντερνετ is the usual, everyday borrowed form from English, written in Greek letters but pronounced almost like English “internet”.

There is also a more “Greek” word:

το διαδίκτυο = the internet (literally “the inter-net”, from Greek roots)

Both are used, but:

στο ίντερνετ sounds more casual and is extremely common in spoken language.
στο διαδίκτυο appears more in formal writing, media, official documents, etc.

Grammatically, they behave the same in this sentence:

στο ίντερνετ
στο διαδίκτυο

Both mean “on the internet / online”.