Η κοπέλα στο βιβλιοπωλείο μου δείχνει ένα βιβλίο στα ελληνικά.

Η is the feminine singular definite article in the nominative case, so here it means the.

So:

• η κοπέλα = the girl

Also, Η is pronounced ee, not like the English letter H.

στο is a contraction of σε + το.

• σε = a very common preposition that can mean in, at, or to
• το = the for a neuter singular noun

So:

• σε το βιβλιοπωλείο becomes στο βιβλιοπωλείο

This kind of contraction is extremely common in Modern Greek:

• στο = σε το
• στη / στην = σε τη / σε την
• στον = σε τον
• στα = σε τα

Here it means in or at, because it shows location, not movement.

So:

• στο βιβλιοπωλείο = in/at the bookstore

Greek σε is broader than English prepositions, so the exact English translation depends on context.

For example:

• Πάω στο βιβλιοπωλείο = I’m going to the bookstore
• Είμαι στο βιβλιοπωλείο = I’m at/in the bookstore

In your sentence, it describes where the girl is.

After σε (and therefore after στο), Modern Greek normally uses the accusative.

So βιβλιοπωλείο here is in the accusative singular.

However, with many neuter nouns, the nominative and accusative forms are the same, so you do not see a change:

• το βιβλιοπωλείο = nominative or accusative, depending on function

That is why it looks unchanged.

In this sentence, the most natural reading is that it describes the girl:

• Η κοπέλα στο βιβλιοπωλείο = the girl in/at the bookstore

So the phrase is understood as identifying which girl.

That said, Greek word order is flexible, and context always matters. If you wanted to make the location of the action more clearly adverbial, you could move it:

• Στο βιβλιοπωλείο, η κοπέλα μου δείχνει ένα βιβλίο.

But in your original sentence, most learners will naturally read it as modifying κοπέλα.

Here μου means to me or simply me in English translation.

So:

• μου δείχνει = shows me

This is a very common point of confusion because μου can also mean my in other contexts:

• το βιβλίο μου = my book

In your sentence, though, μου is not possessive. It is an object pronoun connected to the verb δείχνει.

Because μου is a weak object pronoun (often called a clitic), and in Modern Greek these pronouns usually go before a finite verb.

So Greek says:

• μου δείχνει = literally to-me shows

This is normal Greek word order for clitics.

Compare:

• Μου μιλάει. = He/She is talking to me.
• Μου δίνει ένα βιβλίο. = He/She gives me a book.

One important exception: with affirmative commands, the clitic usually goes after the verb:

• Δείξε μου. = Show me.

Because with verbs like δείχνω (show), Greek uses a form that historically comes from the genitive for the indirect object.

So:

• μου = to me
• σου = to you
• του / της = to him / her
• μας = to us
• σας = to you
• τους = to them

In this sentence:

• μου = the person receiving the showing
• ένα βιβλίο = the thing being shown

So the structure is:

• She shows me a book

δείχνει is the 3rd person singular present tense of δείχνω (to show).

So it means:

• he/she/it shows
• or he/she/it is showing

Greek present tense can cover both simple present and present continuous, depending on context.

Here, δείχνει could be translated as either:

• shows me
• is showing me

ένα is the indefinite article for a neuter singular noun, so it means a.

• ένα βιβλίο = a book

And βιβλίο is a neuter noun.

Again, because it is neuter, the nominative and accusative are the same in form, so:

• ένα βιβλίο looks the same whether it is the subject complement or the direct object

In this sentence, it is the direct object of δείχνει.

στα ελληνικά means in Greek.

It is made of:

• στα = σε + τα
• ελληνικά = Greek, referring to the Greek language

So literally it is something like in the Greek [language].

In natural English:

• ένα βιβλίο στα ελληνικά = a book in Greek
• or a book written in Greek

Because in Greek, names of languages are very often expressed as neuter plural forms with the article.

For example:

• τα ελληνικά = Greek
• τα αγγλικά = English
• τα γαλλικά = French

So even though English uses a singular form like Greek, Greek commonly uses a plural-looking form.

That is why you get:

• στα ελληνικά = in Greek
• literally in the Greek ones/things, from an older adjective-based structure

This is just the normal Greek way to talk about languages.

Greek word order is much more flexible than English word order.

Your sentence is perfectly natural, but other orders are also possible depending on what you want to emphasize.

For example:

• Η κοπέλα στο βιβλιοπωλείο μου δείχνει ένα βιβλίο στα ελληνικά.
• Ένα βιβλίο στα ελληνικά μου δείχνει η κοπέλα στο βιβλιοπωλείο.
• Στο βιβλιοπωλείο, η κοπέλα μου δείχνει ένα βιβλίο στα ελληνικά.

The grammar is carried more by:

• articles
• case
• clitic pronouns
• verb endings

So Greek does not rely on rigid word order as much as English does.

A useful breakdown is:

• Η κοπέλα = the subject, the girl
• στο βιβλιοπωλείο = a prepositional phrase, in/at the bookstore
• μου = indirect object clitic, to me / me
• δείχνει = verb, shows / is showing
• ένα βιβλίο = direct object, a book
• στα ελληνικά = phrase describing the book, in Greek

So the sentence structure is basically:

[subject] + [location/description] + [indirect object] + [verb] + [direct object] + [language phrase]