Μας συμφέρει να πάμε νωρίς στο σούπερ μάρκετ, γιατί μετά έχει πολύ κόσμο.

Μας means to us or for us.

In this sentence, Μας συμφέρει literally means it is advantageous to us, but in natural English it is more like:

• It suits us
• It’s better for us
• It’s in our interest

So Μας is not the subject. It is an object-like pronoun showing who benefits.

You could compare:

• Μου συμφέρει = it suits me
• Σου συμφέρει = it suits you
• Μας συμφέρει = it suits us

Because the real grammatical subject is not we. Greek uses συμφέρει here as an impersonal verb: it is beneficial / it is convenient.

So:

• Μας = to us / for us
• συμφέρει = it is advantageous
• να πάμε νωρίς... = to go early...

Literally: To us, it is advantageous to go early...

That is why the verb stays in 3rd person singular: συμφέρει.

Not exactly.

συμφέρει means something like:

• it is worth it
• it is beneficial
• it is in someone’s interest
• it makes sense practically

πρέπει means:

• must
• should
• ought to

So the difference is:

• Μας συμφέρει να πάμε νωρίς = Going early is a good idea for us / it benefits us.
• Πρέπει να πάμε νωρίς = We have to / should go early.

συμφέρει is about advantage or convenience, not obligation.

Because να introduces the subjunctive in Modern Greek.

After verbs or expressions like:

• θέλω = I want
• μπορώ = I can
• πρέπει = I must
• συμφέρει = it is beneficial

Greek normally uses να + verb.

So:

• Μας συμφέρει να πάμε = It’s better for us to go

In English, we often use to + verb, but Greek uses να + verb form instead.

Because να πάμε refers to a single, complete action: going early on that occasion.

This is the aorist subjunctive of πάω.

• να πάμε = to go, as one whole event
• να πηγαίνουμε = to be going / to go regularly / repeatedly

So in this sentence:

• Μας συμφέρει να πάμε νωρίς = It’s better for us to go early

If you said να πηγαίνουμε νωρίς, it would sound more like a habit:

• It’s better for us to go early in general / regularly

It looks the same, but here it functions differently.

πάμε can be:

• present: we go
• subjunctive form after να: that we go / to go

In να πάμε, it is not a simple present-tense statement. It is part of the subjunctive construction.

So:

• Πάμε στο σούπερ μάρκετ = We go / we’re going to the supermarket
• Να πάμε στο σούπερ μάρκετ = to go to the supermarket / shall we go to the supermarket?

Context tells you which meaning is intended.

νωρίς means early.

It comes after να πάμε because it modifies the action of going:

• να πάμε νωρίς = to go early

This word order is very natural in Greek. Greek word order is fairly flexible, but this version sounds neutral and normal.

You could move it for emphasis, but the standard order here is good:

• να πάμε νωρίς στο σούπερ μάρκετ

στο is a contraction of:

• σε = to / at / in
• το = the

So:

• σε το → στο

Therefore:

• στο σούπερ μάρκετ = to the supermarket / at the supermarket

This contraction is extremely common in Modern Greek.

You will also see:

• στη = σε + τη
• στην = σε + την
• στον = σε + τον

Because σούπερ μάρκετ is a borrowed word and is usually treated as indeclinable in Modern Greek.

That means its form stays the same in different cases:

• το σούπερ μάρκετ
• στο σούπερ μάρκετ
• από το σούπερ μάρκετ

Many loanwords behave this way.

It is usually treated as neuter, which is why the article is το.

Yes. γιατί can mean both:

• because
• why

In this sentence, it clearly means because:

• ..., γιατί μετά έχει πολύ κόσμο.
• ..., because later it gets very crowded / there are lots of people later.

As a question word:

• Γιατί πας; = Why are you going?

The meaning depends on context and punctuation.

μετά here means afterwards, later, or later on.

So:

• γιατί μετά έχει πολύ κόσμο = because later there are a lot of people

It refers to a later time in the day, not necessarily after that exact action in a strict sequence.

In everyday speech, μετά is very commonly used like later.

This is a very common Greek structure.

έχει literally means it has, but in expressions about places or situations it often works like English there is / there are.

So:

• έχει πολύ κόσμο = there are lots of people / it’s crowded

Here έχει does not mean that the supermarket possesses people. It is just the normal Greek way to express that a place is crowded.

You will hear similar phrases like:

• Στο μαγαζί έχει πολύ κόσμο. = The shop is very crowded.
• Σήμερα έχει κίνηση. = There is traffic today.

Because κόσμο here means people / crowd / the public as a collective noun.

So:

• πολύ κόσμο = a lot of people

Even though English uses the plural people, Greek often uses singular κόσμος in this sense.

Also, after έχει, the noun appears in the accusative:

• έχει κόσμο = there are people / it’s busy
• έχει πολύ κόσμο = there are lots of people

This is a very useful everyday expression.

Yes, absolutely.

• μετά = later / afterwards
• αργότερα = later

Both can work here.

The original version with μετά sounds very natural and conversational. Αργότερα can sound a little more explicit or slightly more formal, depending on context.

So both are possible:

• γιατί μετά έχει πολύ κόσμο
• γιατί αργότερα έχει πολύ κόσμο

In normal writing, yes, it is natural to put a comma before γιατί when it introduces a reason clause:

• Μας συμφέρει να πάμε νωρίς στο σούπερ μάρκετ, γιατί μετά έχει πολύ κόσμο.

This is similar to English:

• It’s better for us to go early, because later it gets crowded.

In very informal writing, people may sometimes omit commas, but the standard punctuation with the comma is best.

Yes. The original sentence is already natural, but Greek has a few other everyday ways to express the same idea.

For example:

• Μας συμφέρει να πάμε νωρίς στο σούπερ μάρκετ, γιατί μετά έχει κόσμο.
• Καλύτερα να πάμε νωρίς στο σούπερ μάρκετ, γιατί μετά έχει πολύ κόσμο.
• Ας πάμε νωρίς στο σούπερ μάρκετ, γιατί μετά θα έχει πολύ κόσμο.

Small differences:

• Μας συμφέρει = it’s advantageous / practical for us
• Καλύτερα = better
• Ας πάμε = let’s go

The version you were given is perfectly good and idiomatic.