Η φίλη μου μιλάει με ευκολία όταν ξέρει καλά το θέμα.

Yes, literally it is the friend my, but in natural English it means my friend.

In Greek, possessive pronouns like μου often come after the noun:

• η φίλη μου = my friend
• το βιβλίο μου = my book

The article η is normally kept:

• η φίλη μου = my friend not just φίλη μου in neutral standard usage.

Also, φίλη is feminine, so this means my female friend.
For a male friend, you would say ο φίλος μου.

Φίλη is the feminine form of friend:

• ο φίλος = male friend
• η φίλη = female friend

So the sentence tells you that the friend being talked about is female.

This affects:

• the article: η
• the noun ending: -η

Greek nouns usually show grammatical gender clearly, and articles must match them.

Μιλάει means he/she/it speaks or is speaking, depending on context.
Here it means she speaks.

The verb is μιλάω / μιλώ = to speak.

Common present-tense forms:

• μιλάω / μιλώ = I speak
• μιλάς = you speak
• μιλάει / μιλά = he/she speaks
• μιλάμε / μιλούμε = we speak
• μιλάτε / μιλείτε = you plural speak
• μιλάνε / μιλούν = they speak

So μιλάει and μιλά are both acceptable forms for he/she speaks.
Μιλάει is very common in everyday Greek.

Yes. Με ευκολία literally means with ease.

So:

• μιλάει με ευκολία = she speaks with ease
• more naturally in English: she speaks easily

Greek often uses με + noun where English might prefer an adverb:

• με ευκολία = easily / with ease
• με δυσκολία = with difficulty

So this is a very natural Greek expression.

Yes, it could.

• μιλάει εύκολα = she speaks easily
• μιλάει με ευκολία = she speaks with ease

Both are correct, but the nuance is a little different:

• εύκολα is the straightforward adverb
• με ευκολία can sound a bit more descriptive or formal

In this sentence, με ευκολία emphasizes that speaking is easy for her.

Όταν means when.

It introduces the time clause:

• όταν ξέρει καλά το θέμα = when she knows the subject well

So the whole sentence means something like:

• My friend speaks with ease when she knows the subject well.

Greek uses όταν very commonly for when in situations like this.

Ξέρει means she knows.

The verb is ξέρω = to know.

Here:

• ξέρει καλά το θέμα = she knows the subject well

Greek ξέρω is often used for knowing facts, information, or being familiar with something. In this sentence, it means she knows the topic well enough to speak about it confidently.

Here καλά modifies ξέρει, not θέμα.

So:

• ξέρει καλά = knows well

Then:

• ξέρει καλά το θέμα = she knows the topic well

This word order is normal in Greek.
You can think of it as:

• ξέρει = knows
• καλά = well
• το θέμα = the subject/topic

So the sense is she knows the topic well, not the good topic.

All of those can be possible translations depending on context, but here θέμα most naturally means topic or subject.

So:

• το θέμα = the topic / the subject

In this sentence, it means the matter she is talking about.
If she knows the topic well, she speaks easily.

Because Greek usually does not need subject pronouns when the verb already shows the person.

• μιλάει already tells you it is he/she/it speaks
• from η φίλη μου, you know the subject is feminine singular, so in context it means she

Greek often leaves out pronouns like εγώ, εσύ, αυτός, αυτή unless they are needed for emphasis or contrast.

So Greek prefers:

• Η φίλη μου μιλάει...

rather than:

• Η φίλη μου αυτή μιλάει...
  which would sound unnecessary here.

Greek word order is more flexible than English word order, because endings and articles show grammatical relationships.

The given sentence is very natural:

• Η φίλη μου μιλάει με ευκολία όταν ξέρει καλά το θέμα.

But other orders may also be possible for emphasis, for example:

• Όταν ξέρει καλά το θέμα, η φίλη μου μιλάει με ευκολία.

That puts more focus on the condition when she knows the topic well.

So the original order is neutral and natural, but Greek can move parts around more easily than English.

A rough pronunciation is:

ee FEE-lee moo mee-LA-ee me ev-ko-LEE-a O-tan KSE-ri ka-LA to THE-ma

A few notes:

• η sounds like ee
• φ sounds like f
• ξ sounds like ks
• θ sounds like the th in think
• stress matters in Greek:
  • φίλη
  • μιλάει
  • ευκολία
  • όταν
  • ξέρει
  • καλά
  • θέμα

Most naturally, it describes a general tendency or habit:

• My friend speaks with ease when she knows the subject well.

That means this is generally true about her.

Greek present tense often covers:

• habitual actions
• general truths
• present situations

So without extra context, this sounds like a general statement, not just one single moment.