Η φίλη μου δεν ήξερε τι να γράψει στο έγγραφο για το δημαρχείο.

In Greek, the definite article is very often used with possessives.

So:

• η φίλη = the friend
• η φίλη μου = my friend

Even though English does not say the my friend, Greek normally does use the article here. This is completely natural Greek.

Because φίλη is feminine singular, the article is η.

μου is the weak possessive form meaning my. In Greek, these weak possessives usually come after the noun:

• η φίλη μου = my friend
• το σπίτι μου = my house
• η αδερφή μου = my sister

So Greek says something closer to the friend my in word order, even though the natural English translation is my friend.

It can mean either, depending on context.

• η φίλη μου can mean my female friend
• It can also mean my girlfriend

Greek often relies on context to make the difference clear. In a neutral sentence like this one, it may simply mean my friend if the person is female. If the broader context is romantic, then it could mean my girlfriend.

ήξερε is the imperfect past of ξέρω (to know). The imperfect is used for:

• ongoing situations in the past
• states in the past
• background information

So δεν ήξερε means she didn’t know in the sense of a state: she was in a situation where she did not know.

That fits very well with knowing because knowing is usually treated as a state, not as a one-time completed action.

So:

• δεν ήξερε τι να γράψει = she didn’t know what to write

In standard Greek, δεν is the normal negation used with indicative verb forms, and it comes before the verb:

• δεν ξέρω = I don’t know
• δεν ήξερε = she didn’t know

That is just the standard position for negation in Greek.

τι να γράψει literally means something like what she should write or what to write.

Greek does not have an infinitive like English to write in this kind of structure, so it often uses:

• question word + να
  • subjunctive verb

Examples:

• τι να κάνω = what to do / what should I do
• πού να πάμε = where to go / where should we go
• τι να γράψει = what to write / what she should write

So in this sentence:

• δεν ήξερε τι να γράψει = she didn’t know what to write

This is a very common Greek pattern.

Because after να, Greek normally uses the subjunctive, not the indicative.

Here:

• γράψει = subjunctive form
• γράφει = indicative present (she writes / is writing)
• έγραψε = simple past (she wrote)

So after τι να..., you need the subjunctive form.

Also, γράψει here is the aorist subjunctive, which usually presents the action as a single whole action: what to write. That sounds natural, because writing something in the document is viewed as a complete act.

στο is a contraction of:

• σε
  • το = στο

So:

• στο έγγραφο = in/on the document

Greek very commonly combines σε with the definite article:

• στο σπίτι = at/in the house
• στην πόλη = in the city
• στο βιβλίο = in the book

Greek σε is broader than any one English preposition. Depending on context, it can correspond to:

• in
• on
• at
• sometimes other location-related prepositions

So στο έγγραφο could be translated as:

• in the document
• on the document

The correct English choice depends on context, but the Greek expression itself is normal.

Greek uses the definite article much more often than English.

So if a specific document or a specific institution is meant, Greek naturally says:

• στο έγγραφο = in/on the document
• για το δημαρχείο = for the town hall / city hall

Even where English might sometimes leave the article out, Greek often keeps it.

για most often means for, but it can also mean about, depending on context.

Here για το δημαρχείο most naturally means:

• for the town hall / city hall

In other words, the document is intended for that office or institution.

Vocabulary:

• δημαρχείο = town hall / city hall / municipal building

So the phrase likely means the document was meant to be submitted to, sent to, or used for the town hall.

It is a very normal, neutral Greek word order:

• Η φίλη μου = subject
• δεν ήξερε = verb
• τι να γράψει = embedded clause
• στο έγγραφο = where to write
• για το δημαρχείο = what the document is for

Greek word order is more flexible than English, but this sentence is straightforward and unmarked. It sounds like standard everyday Greek.

Because δημαρχείο is a neuter noun, so it takes the neuter article το:

• το δημαρχείο

Many Greek nouns ending in -είο are neuter:

• το σχολείο = the school
• το μουσείο = the museum
• το δημαρχείο = the town hall

So the gender here is just part of the noun and must be learned with it.