Learn Hardcore Greek: Στην περιοχή αυτή μένει πολύς κόσμος, αλλά το βράδυ είναι ήσυχα και μπροστά από το σπίτι μου έχει ένα μεγάλο δέντρο. - In this area many people live, but in the evening it is quiet and in front of my house there is a big tree.

In modern Greek, the accusative singular of this noun is την περιοχή (no final -ν on the noun itself).
The preposition σε almost always takes the accusative case.

So:

Στην περιοχή = in the area
(σε
- την περιοχή → στην περιοχή)

Why is it Στην περιοχή αυτή and not Αυτή η περιοχή? Is there a difference?

Both are correct, but the word order is slightly different in nuance:

Αυτή η περιοχή – more neutral, common order: demonstrative + article + noun
- Literally: this the area
Η περιοχή αυτή or Στην περιοχή αυτή – demonstrative after the noun
- Slightly more “pointing” or contrastive: this area (as opposed to some other one)

In your sentence:

Στην περιοχή αυτή μένει πολύς κόσμος…
could also be:
Σε αυτή την περιοχή μένει πολύς κόσμος…

Meaning is practically the same; Στην περιοχή αυτή just feels a bit more “literary” or emphatic.

Why is the verb μένει (3rd person singular) when πολύς κόσμος means “a lot of people”? Shouldn’t it be plural?

In Greek, κόσμος is grammatically singular, even when it means “people”.

πολύς κόσμος = a lot of people
- κόσμος: masculine, singular
- so the verb agrees in singular: ο κόσμος μένει → μένει

You would only use a plural verb if the subject itself were grammatically plural, for example:

Πολλοί άνθρωποι μένουν στην περιοχή αυτή.
Many people live in this area.
- άνθρωποι is plural → μένουν.

Why πολύς κόσμος and not πολλοί κόσμος or πολύ κόσμο?

All three forms exist, but they’re used differently:

πολύς κόσμος
- Grammatically: adjective πολύς (masc. sg.) + noun κόσμος (masc. sg.)
- Very standard: a lot of people.
πολύ κόσμο
- πολύ (invariable form) + κόσμο (accusative)
- Common especially after verbs that often take an object:
  - Είδα πολύ κόσμο. = I saw a lot of people.
πολλοί κόσμος
- This is wrong, because πολλοί is masculine plural, but κόσμος is masculine singular.
- You could say πολλοί άνθρωποι, but not πολλοί κόσμος.

So in your sentence, πολύς κόσμος is the correct subject phrase.

Why do we use κόσμος for “people” instead of άνθρωποι?

In Greek, κόσμος can mean:

world (the world)
people, “the public”, “everyone around”

So:

Μένει πολύς κόσμος.
= A lot of people live (here).

If you say:

Μένουν πολλοί άνθρωποι.
= Many people live (here).

The second is a bit more literal; κόσμος is very common and sounds very natural in everyday Greek when you mean “a lot of people in general”.

Why do we say το βράδυ instead of just βράδυ?

Greek often uses the definite article το with parts of the day in time expressions:

το πρωί – in the morning
το μεσημέρι – at noon / midday
το απόγευμα – in the afternoon
το βράδυ – in the evening / at night

So το βράδυ είναι ήσυχα is the natural way to say:

At night it is quiet.

You can sometimes drop the article in very casual speech (βράδυ είναι ήσυχα), but το βράδυ is more standard.

Why is it είναι ήσυχα and not είναι ήσυχο or είναι ήσυχος?

Here ήσυχα is the adverbial form of the adjective ήσυχος (quiet).

ήσυχος (m.), ήσυχη (f.), ήσυχο (n.) – adjective: quiet
ήσυχα – adverb-like form: quietly / it is quiet (in general)

Greek often forms adverbs from adjectives with a neuter plural-looking ending:

καλός → καλά (well, nicely)
κακός → κακά (badly, badly)
όμορφος → όμορφα (beautifully)
ήσυχος → ήσυχα (quietly / things are quiet)

In Το βράδυ είναι ήσυχα, there is no specific noun as subject like “the street” or “the area”; it means more generally:

At night, it’s quiet (things are quiet).

If you wanted a specific subject, you’d use the adjective form, for example:

Η περιοχή είναι ήσυχη. – The area is quiet.
Το μέρος είναι ήσυχο. – The place is quiet.

Can I say Το βράδυ η περιοχή είναι ήσυχη instead of το βράδυ είναι ήσυχα? Is there a difference?

Yes, you can say that, and both are correct, but the focus is a bit different:

Το βράδυ είναι ήσυχα.
- Very general: At night it’s quiet (around here/in general).
- No explicit subject; the situation or environment is quiet.
Το βράδυ η περιοχή είναι ήσυχη.
- Explicit subject: At night the area is quiet.
- You’re specifically describing η περιοχή.

Your original sentence uses the more general, impersonal style (είναι ήσυχα).

Why do we say μπροστά από το σπίτι and not just μπροστά το σπίτι?

The word μπροστά by itself is an adverb: in front / ahead.
To say “in front of something”, Greek normally uses:

μπροστά από + accusative

So:

μπροστά από το σπίτι μου = in front of my house

Without από, μπροστά το σπίτι would be ungrammatical: το σπίτι would just look like a random noun after the adverb.

What is the difference between μπροστά από το σπίτι μου and μπροστά στο σπίτι μου?

Both are used and often interchangeable, but there’s a nuance:

μπροστά από το σπίτι μου
- Literally: in front from my house
- Often slightly more about position relative to the house, can feel a bit more general.
μπροστά στο σπίτι μου (μπροστά σε + το → στο)
- Literally: in front at my house
- Often feels a bit more immediate / closer: right in front of the house.

In everyday speech, many people will use both without a strong difference in meaning. Your sentence with μπροστά από το σπίτι μου is perfectly natural.

Why is it το σπίτι μου and not μου το σπίτι, since English says “my house”?

In Greek, possessive pronouns like μου, σου, του, της, μας, σας, τους usually come after the noun:

το σπίτι μου – my house
η φίλη σου – your friend
το βιβλίο μας – our book

The order μου το σπίτι is possible only in very specific emphatic or poetic contexts and sounds unnatural here. The normal pattern is:

article + noun + possessive → το σπίτι μου

Why do we use έχει for “there is” in μπροστά από το σπίτι μου έχει ένα μεγάλο δέντρο? Isn’t έχει just “has”?

Yes, έχει basically means “has”, but in everyday Greek it is also used impersonally to mean “there is / there are”.

Έχει ένα μεγάλο δέντρο μπροστά από το σπίτι μου.
= There is a big tree in front of my house.

This is very common in spoken Greek. There is no explicit subject; it’s like saying “it has…here”.

You could also use υπάρχει, which is more formal or explicit:

Μπροστά από το σπίτι μου υπάρχει ένα μεγάλο δέντρο.
= There is a big tree in front of my house.

Both are correct; έχει is more colloquial.

Could we say υπάρχει ένα μεγάλο δέντρο instead of έχει ένα μεγάλο δέντρο? Any difference in meaning?

Yes, you can say:

Μπροστά από το σπίτι μου υπάρχει ένα μεγάλο δέντρο.

Meaning-wise, it’s the same: There is a big tree in front of my house.

Nuance:

έχει – very common in speech, neutral, everyday
υπάρχει – a bit more formal / explicit about existence, common in written language, explanations, etc.

In conversation, έχει feels more natural in many regions.

Why is it ένα μεγάλο δέντρο and not μεγάλο ένα δέντρο? Where do adjectives go?

The normal position of an adjective in Greek is before the noun, after the article:

ένα μεγάλο δέντρο – a big tree
το κόκκινο αυτοκίνητο – the red car
ένας καλός φίλος – a good friend

So the pattern is:

article + adjective + noun

You can sometimes put the adjective after the noun (το δέντρο το μεγάλο) for emphasis or a slightly different nuance, but:

μεγάλο ένα δέντρο is not a normal noun phrase in standard Greek.

Why do we need the article ένα in ένα μεγάλο δέντρο? Can we just say μεγάλο δέντρο?

Greek almost always uses the indefinite article (ένας, μία/μια, ένα) with a countable singular noun when you mean “a / one” in a specific sense.

Έχει ένα μεγάλο δέντρο. – There is a big tree.
Έχει μεγάλο δέντρο. – Feels incomplete / unusual in this context; could sound more like you’re describing a type (“it has big-tree [kind of tree]”).

Without ένα, the phrase becomes either:

very stylized, or
more about a quality than about “one concrete object”.

So here, to mean “a (single) big tree”, ένα μεγάλο δέντρο is the natural form.