Η αρραβωνιαστικιά μου βρήκε ένα όμορφο δαχτυλίδι στο κέντρο.

Yes. Η αρραβωνιαστικιά μου means my fiancée: the woman someone is engaged to marry.

A few related forms:

• αρραβωνιαστικιά = fiancée / bride-to-be
• αρραβωνιαστικός = fiancé

In everyday English, many learners just think of it as my fiancée.

Η is the definite article for a feminine singular noun in the nominative case. Here it goes with αρραβωνιαστικιά.

So:

• η αρραβωνιαστικιά = the fiancée
• η αρραβωνιαστικιά μου = my fiancée

Greek usually uses the article much more often than English does, including with possessive expressions like my fiancée.

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

So:

• η αρραβωνιαστικιά μου = my fiancée
• το σπίτι μου = my house
• η τσάντα της = her bag

This is one of the most important word-order differences from English.

Βρήκε is the aorist form of βρίσκω (to find).

So:

• βρίσκω = I find / I am finding
• βρήκα = I found
• βρήκε = he/she/it found

In this sentence, βρήκε means found as a completed action in the past:

• Η αρραβωνιαστικιά μου βρήκε... = My fiancée found...

Because the verb ending already shows the person and number.

Βρήκε is the third person singular form, so it can mean:

• he found
• she found
• it found

The subject η αρραβωνιαστικιά μου makes it clear that it means she found.

Greek often leaves out subject pronouns like αυτή (she) when the verb form already tells you who is doing the action.

Because δαχτυλίδι is a neuter singular noun, so both the article and adjective must match it.

Breakdown:

• ένα = a / one for a neuter singular noun
• όμορφο = beautiful, in the neuter singular form
• δαχτυλίδι = ring, a neuter singular noun

So:

• ένα όμορφο δαχτυλίδι = a beautiful ring

This is adjective agreement:

• masculine noun -> masculine adjective form
• feminine noun -> feminine adjective form
• neuter noun -> neuter adjective form

It can mean both, depending on context.

Here, ένα όμορφο δαχτυλίδι most naturally means:

• a beautiful ring

But ένα can also mean one if you want to emphasize number:

• βρήκε ένα δαχτυλίδι, όχι δύο = she found one ring, not two

In this sentence, it is usually understood simply as the indefinite article a.

It is in the accusative singular, because it is the direct object of βρήκε.

The useful thing is that many neuter nouns in Greek look the same in the nominative and accusative singular.

So:

• nominative: το δαχτυλίδι
• accusative: το δαχτυλίδι

That is why the form does not change here, even though its grammatical role is different.

Στο κέντρο means in the center or downtown / in the city center, depending on context.

It is made of:

• σε = in / at / to
• το = the
• στο = contraction of σε + το

And:

• κέντρο = center

So literally:

• στο κέντρο = in the center

In natural usage, it often means:

• in the town/city center
• downtown

Because in normal Greek, σε + the article usually contracts:

• σε + το = στο
• σε + τη(ν) = στη(ν)
• σε + τον = στον
• σε + τα = στα

So instead of σε το κέντρο, Greek normally says:

• στο κέντρο

This is the standard form you should learn and use.

Yes. Greek word order is more flexible than English word order, although the original sentence is completely natural.

Original:

• Η αρραβωνιαστικιά μου βρήκε ένα όμορφο δαχτυλίδι στο κέντρο.

Other possible orders, depending on emphasis:

• Στο κέντρο η αρραβωνιαστικιά μου βρήκε ένα όμορφο δαχτυλίδι.
• Ένα όμορφο δαχτυλίδι βρήκε η αρραβωνιαστικιά μου στο κέντρο.

The basic meaning stays the same, but the focus changes. English is less flexible here, so learners often need time to get used to Greek emphasis through word order.

A rough pronunciation guide is:

ee ar-ra-vo-nya-STEE-kya moo VREE-ke ENA O-mor-fo tha-hee-THEE-lee stoh KEN-dro

A few notes:

• η sounds like ee
• για in αρραβωνιαστικιά sounds roughly like ya
• βρ in βρήκε is pronounced together at the start
• χτ in δαχτυλίδι can be tricky for English speakers
• δ in Modern Greek is like th in this, not like English d

You do not need the rough guide forever, but it can help at first.

Normally it attaches to the action βρήκε:

• My fiancée found a beautiful ring in the center / downtown

So it tells you where she found it.

In theory, context could sometimes make a phrase like this describe the noun, but in this sentence the most natural reading is that στο κέντρο describes the location of the finding, not the location of the ring as a permanent characteristic.

Yes, they matter in standard written Greek.

For example:

• αρραβωνιαστικιά
• βρήκε
• όμορφο
• δαχτυλίδι
• κέντρο

Accent marks show which syllable is stressed, and stress is important for correct pronunciation. Even if people may still understand you without perfect accents in informal typing, you should learn the correct accented forms.