Όταν φιλοξενώ κόσμο, προσφέρω πρώτα νερό ή καφέ.

Όταν can mean when, but in a sentence like this it often has the sense of whenever.

So:

• Όταν φιλοξενώ κόσμο... = When / Whenever I have guests over...

Because the rest of the sentence describes a usual habit, English would often translate it as whenever.

Φιλοξενώ means to host, to have someone over, or to offer hospitality.

It comes from the Greek idea of hospitality:

• φιλοξενία = hospitality
• φιλοξενώ = I host / I accommodate guests

In this sentence, it means something like:

• When I have people over
• When I host guests

Φιλοξενώ is:

• 1st person singular
• present tense
• active voice

So it means I host or I am hosting, depending on context. Here it expresses a habitual action:

• When I host people, I offer water or coffee first.

Greek present tense often covers both:

• simple present: I host
• habitual present: I usually host / when I host
• sometimes present continuous: I am hosting

Yes, κόσμος can mean world, but it also very commonly means:

• people
• crowd
• guests / company in the right context

Here, φιλοξενώ κόσμο means:

• I have people over
• I host guests
• literally, I host people

This is a very common use of κόσμος in everyday Greek.

Because κόσμο is the accusative singular form, and it is the direct object of φιλοξενώ.

The basic form is:

• ο κόσμος = the people / the world / the crowd

But after a verb, as a direct object, Greek usually uses the accusative:

• φιλοξενώ κόσμο = I host people

This is also an example where Greek often uses the singular noun collectively, even though English would often say people.

Greek often leaves out the article when speaking in a general, non-specific way.

So:

• φιλοξενώ κόσμο = I host people / I have guests over
• not necessarily the people or some specific people

If you added an article, it would sound more specific:

• φιλοξενώ τον κόσμο would usually mean I host the people or something context-specific, and in many contexts it would sound odd.

So the article is omitted because the meaning is general.

Προσφέρω means I offer.

In this sentence:

• προσφέρω πρώτα νερό ή καφέ = I offer water or coffee first

It is also:

• 1st person singular
• present tense
• active voice

So both main verbs in the sentence are in the same form:

• φιλοξενώ = I host
• προσφέρω = I offer

Because πρώτα here is an adverb, not an adjective.

It means:

• first

Compare:

• ο πρώτος καφές = the first coffee
  (πρώτος = adjective)
• προσφέρω πρώτα καφέ = I offer coffee first
  (πρώτα = adverb)

So in this sentence, πρώτα tells us when / in what order the offering happens.

Because in Greek, just like in English, food and drink items are often used without an article when speaking generally.

So:

• νερό ή καφέ = water or coffee

This sounds natural because the speaker means:

• some water
• some coffee

not a specific water or a specific coffee.

If you added articles:

• το νερό ή τον καφέ it would sound more specific and less natural in this general hospitality sentence.

Καφές is the basic dictionary form (nominative singular), but here the word is the object of the verb προσφέρω, so it appears in the accusative:

• ο καφές = coffee / the coffee
• τον καφέ = coffee / the coffee (object form)

When the article is omitted, the noun still stays in the accusative form:

• προσφέρω καφέ = I offer coffee

So καφέ is the correct object form.

Good question. Νερό is a neuter noun, and many neuter nouns have the same form in nominative and accusative singular.

So:

• το νερό = the water
• προσφέρω νερό = I offer water

There is no visible change in the noun itself, unlike with καφές → καφέ.

Yes, Greek word order is flexible, though the original order sounds very natural.

Original:

• Όταν φιλοξενώ κόσμο, προσφέρω πρώτα νερό ή καφέ.

This is a normal, neutral way to say it.

You could also hear:

• Όταν φιλοξενώ κόσμο, πρώτα προσφέρω νερό ή καφέ.
• Πρώτα προσφέρω νερό ή καφέ όταν φιλοξενώ κόσμο.

These are all possible, but the original sentence has a smooth, natural rhythm and gives the idea clearly.

Ή simply means or.

In this sentence, it means the host offers water or coffee, depending on the situation or the guest’s preference. It does not necessarily mean a strict logical either/or. It is just the normal everyday or.

It describes a general habit.

The clues are:

• Όταν introducing a repeated situation
• both verbs in the present tense
• the sentence expresses what the speaker normally does

So the sense is:

• Whenever I have guests over, I first offer water or coffee.

Yes. While I host people is close to the Greek structure, more natural English translations might be:

• When I have guests over...
• When I have people over...
• When I’m entertaining guests...

Greek often uses κόσμο in a way that sounds very natural, but English usually prefers guests or people over in this context.