Ο πατέρας μου έχει επιχείρηση.

Ο is the masculine singular definite article in the nominative case. It means the, but in Greek the article is used more often than in English.

So ο πατέρας μου literally looks like the father of me, but it naturally means my father.

In this sentence:

• ο = masculine singular nominative article
• πατέρας = father
• μου = my

So the whole phrase ο πατέρας μου means my father.

In Greek, short possessive words like μου (my), σου (your), and του/της (his/her) usually come after the noun.

So:

• ο πατέρας μου = my father
• η μητέρα μου = my mother
• το σπίτι μου = my house

This is one of the first word-order differences English speakers notice, because English says my father, while Greek usually says something more like the father my.

Πατέρας is in the nominative singular, because it is the subject of the sentence.

The subject is the person or thing doing the action:

• Ο πατέρας μου = the subject
• έχει = has
• επιχείρηση = business

So πατέρας is in the form used for the subject of the sentence.

Έχει is the 3rd person singular present form of the verb έχω (to have).

So:

• έχω = I have
• έχεις = you have
• έχει = he/she/it has

In this sentence, the subject is ο πατέρας μου (my father), which is he, so Greek uses έχει.

Because Modern Greek does not have an indefinite article like English a/an.

So:

• έχει επιχείρηση literally = has business
• but in natural English this means has a business

Greek often uses a bare noun where English needs a or an.

Compare:

• Έχω αυτοκίνητο. = I have a car.
• Έχει σπίτι. = He/She has a house.
• Ο πατέρας μου έχει επιχείρηση. = My father has a business.

Επιχείρηση usually means business, company, or enterprise, depending on context.

In this sentence, the most natural translation is business:

• Ο πατέρας μου έχει επιχείρηση. = My father has a business.

It can refer to a commercial business in general, not necessarily a huge corporation.

A useful detail:

• η επιχείρηση = the business
  So the noun is feminine.

It is not την επιχείρηση because that would mean the business, referring to a specific business already known in context.

It is not μια επιχείρηση because although μια can sometimes mean one and can also function like a/an in some contexts, Greek very often simply leaves it out after verbs like have.

So:

• έχει επιχείρηση = has a business
• έχει μια επιχείρηση = also possible, but often a bit more specific or emphatic, like has a business / does have a business / has one business

The version in your sentence is very normal and natural.

Greek word order is more flexible than English word order.

The neutral order here is:

• Ο πατέρας μου έχει επιχείρηση.

But Greek can also change the order for emphasis, for example:

• Έχει επιχείρηση ο πατέρας μου.
  = My father has a business / It’s my father who has a business
• Επιχείρηση έχει ο πατέρας μου.
  = emphasizes business

Even when the order changes, the meaning usually stays understandable because Greek endings and articles give grammatical clues.

A simple pronunciation guide is:

O pa-THE-ras moo E-hi epi-HEE-ri-si

A few notes:

• ο sounds like o in not (depending on accent)
• πατέρας is stressed on τέ
• μου sounds like moo
• έχει is stressed on the first syllable: E-hi
• επιχείρηση is stressed on χεί: epi-HEE-ri-si

The Greek stress marks show which syllable gets the stress:

• πατέρας
• έχει
• επιχείρηση

In standard Greek, that would usually sound wrong or incomplete in a normal sentence.

Greek normally needs the article with a noun like this:

• ο πατέρας μου

So the standard form is:

• Ο πατέρας μου έχει επιχείρηση.

English speakers often want to drop the article because English says my father, not the my father, but in Greek the article is part of the normal structure.

Πατέρας is usually closer to father in style, though in many everyday contexts it can still simply mean dad depending on tone and situation.

A more informal and everyday word is:

• μπαμπάς = dad

So you could also hear:

• Ο μπαμπάς μου έχει επιχείρηση.

That sounds more conversational and family-like:

• ο πατέρας μου = my father
• ο μπαμπάς μου = my dad

The accent marks in Greek show which syllable is stressed.

So:

• έχει → stress on the first syllable
• επιχείρηση → stress on χεί
• πατέρας → stress on τέ

Stress matters in Greek pronunciation, and sometimes it can also help distinguish different forms.

So when reading Greek, it is important to pay attention to the accents, not ignore them.

You would say:

Ο πατέρας μου δεν έχει επιχείρηση.

Here:

• δεν = not / doesn’t
• έχει = has

So:

• Ο πατέρας μου έχει επιχείρηση. = My father has a business.
• Ο πατέρας μου δεν έχει επιχείρηση. = My father does not have a business.