Η φίλη μου ακουμπάει το κεφάλι της στον καναπέ όταν είναι κουρασμένη.

Greek normally uses the definite article with nouns much more often than English does.

So:

• η φίλη μου = my (female) friend
• literally: the friend of mine

This is completely normal Greek. The same happens in:

• το κεφάλι της = her head
• literally: the head of her

So even though English drops the, Greek usually keeps the article.

φίλη is the feminine form of friend.

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

So this sentence specifically tells you the friend is female.
Because φίλη is feminine singular, later words referring to her can also appear in the feminine, such as κουρασμένη.

In Greek, unstressed possessive pronouns like μου, σου, του, της, μας, σας, τους usually come after the noun.

So:

• η φίλη μου = my friend
• το σπίτι του = his house
• η μητέρα μας = our mother

This is the normal word order.
Putting the possessive elsewhere is possible only in special cases for emphasis or in different structures, but for basic Greek, think:

article + noun + possessive

ακουμπάει means something like:

• rests
• leans
• places against
• puts down on

In this sentence, ακουμπάει το κεφάλι της στον καναπέ means she rests/leans her head on the couch.

The verb ακουμπάω / ακουμπώ can be used in a few related ways:

• Ακουμπάει το βιβλίο στο τραπέζι. = She puts the book on the table.
• Ακουμπάει στον τοίχο. = He leans against the wall.
• Μην το ακουμπάς. = Don’t touch it / don’t put your hand on it.

So the exact English translation depends on context.

ακουμπάει is the 3rd person singular present tense form:

• I rest/lean = ακουμπάω / ακουμπώ
• you rest/lean = ακουμπάς
• he/she/it rests/leans = ακουμπάει (also often ακουμπά)

Since the subject is η φίλη μου = my friend / she, Greek uses the he/she form.

So:

• Η φίλη μου ακουμπάει... = My friend rests/leans...

Yes, in everyday Modern Greek, ακουμπάει and ακουμπά are both used for he/she rests/leans/puts.

For many verbs in -άω / -ώ, you can hear or see two common present forms:

• αγαπάει / αγαπά
• μιλάει / μιλά
• ακουμπάει / ακουμπά

Both are standard in modern usage, though style, region, and personal preference can affect which one is more common.

Again, Greek normally keeps the article with body parts and possessed nouns.

So:

• το κεφάλι της = her head
• τα χέρια μου = my hands
• τα μάτια του = his eyes

This is one of the biggest differences from English.
English often says:

• her head
• my hands

But Greek usually says:

• the head her
• the hands my

That is just how possession is commonly expressed.

της means her here. It refers back to η φίλη μου.

So:

• η φίλη μου = my female friend
• το κεφάλι της = her head

Be careful: της can mean different things in different contexts, such as:

• of her
• to her
• sometimes its, for feminine nouns

But in το κεφάλι της, it clearly means her in the possessive sense.

στον is a contraction of:

• σε + τον = στον

Here, σε means on / in / at / to, depending on context.

So:

• στον καναπέ = on the couch / onto the couch

Because καναπές is a masculine noun, the article is τον, and with σε it becomes στον.

Compare:

• στον καναπέ = on the couch (masculine)
• στην καρέκλα = on the chair (feminine)
• στο τραπέζι = on the table (neuter)

The basic dictionary form is:

• ο καναπές = the couch/sofa

But after στον, the noun is in the accusative case:

• nominative: ο καναπές
• accusative: τον καναπέ

Since στον = σε + τον, you get:

• στον καναπέ

This is very common with masculine nouns ending in -ης:

• ο μαθητής → τον μαθητή
• ο καναπές → τον καναπέ

Yes, Greek uses the present here just like English does.

• όταν = when
• είναι = she is
• κουρασμένη = tired

So:

• όταν είναι κουρασμένη = when she is tired

This describes a habitual or general situation: whenever she is tired, she rests her head on the couch.

Greek often uses the present tense for repeated actions or general truths, just as English does in sentences like:

• When she is tired, she drinks tea.
• When I am stressed, I walk.

Because κουρασμένη describes η φίλη μου, not το κεφάλι της.

The adjective must agree with the noun it refers to:

• η φίλη is feminine singular
• so the adjective is κουρασμένη = feminine singular

Forms:

• κουρασμένος = masculine
• κουρασμένη = feminine
• κουρασμένο = neuter

So the sentence means:

• when she is tired

not

• when her head is tired

Yes. The core sentence is:

• Η φίλη μου ακουμπάει το κεφάλι της στον καναπέ.
• My friend rests her head on the couch.

The part:

• όταν είναι κουρασμένη
• when she is tired

just adds the circumstance or condition under which this happens.

So the sentence is built like this:

1. Η φίλη μου = subject
2. ακουμπάει = verb
3. το κεφάλι της = object
4. στον καναπέ = location/direction
5. όταν είναι κουρασμένη = time/circumstance clause

In this sentence, the most natural English translation is probably on the couch or against the couch, depending on the exact image.

Because ακουμπάω can mean rest/lean/place against, Greek leaves some flexibility here.

Possible interpretations:

• she lays her head on the couch
• she leans her head against the couch
• she rests her head on/against the couch

So the exact English wording depends a bit on context, but the Greek is perfectly natural.

Greek often does not use subject pronouns unless they are needed for emphasis or contrast.

The verb form ακουμπάει already tells you the subject is:

• he / she / it

And the noun η φίλη μου already makes it clear who the subject is.

So Greek does not need to add αυτή for she.

Using αυτή would sound emphatic, like:

• She rests her head on the couch...

But in a normal sentence, it is unnecessary.