Αγόρασα σαμπουάν και οδοντόκρεμα από το σούπερ μάρκετ, γιατί και τα δύο είχαν τελειώσει.

Αγόρασα is the simple past (aorist) of αγοράζω = I buy.

• αγοράζω = I buy / I am buying
• αγόραζα = I was buying / I used to buy
• αγόρασα = I bought

Here the speaker is talking about one completed action in the past, so αγόρασα is the natural choice.

Greek often drops subject pronouns when they are not needed, because the verb ending already shows the person.

• Αγόρασα already means I bought
• If you said Εγώ αγόρασα, that would add emphasis: I bought

So leaving out εγώ is completely normal.

In Greek, just like in English, you often do not use an article when talking about indefinite things after a verb like buy.

So:

• Αγόρασα σαμπουάν = I bought shampoo
• Αγόρασα οδοντόκρεμα = I bought toothpaste

If you added articles, it would sound more like the shampoo or a specific shampoo/toothpaste, depending on context.

• το σαμπουάν is neuter
• η οδοντόκρεμα is feminine

A learner may notice that the sentence does not show the articles before these nouns, but their genders still matter in other contexts.

For example:

• Το σαμπουάν είναι ακριβό. = The shampoo is expensive.
• Η οδοντόκρεμα είναι στο μπάνιο. = The toothpaste is in the bathroom.

από usually means from, and here it marks the place of purchase/source:

• από το σούπερ μάρκετ = from the supermarket

Greek often uses από in places where English might say at or just leave it implied.

Also, από is followed by the accusative, so:

• το σούπερ μάρκετ stays το σούπερ μάρκετ

Many foreign words like σούπερ μάρκετ do not change form.

Greek uses the definite article very frequently, including with many places and nouns where English might omit it.

So Greek says:

• το σούπερ μάρκετ = the supermarket

Even if English sometimes says from supermarket in a note-like style, normal Greek wants the article here.

Yes. γιατί can mean either:

• because
• why

In this sentence, it clearly means because:

• ..., γιατί και τα δύο είχαν τελειώσει.
• ..., because both had run out.

As a question word:

• Γιατί αγόρασες σαμπουάν; = Why did you buy shampoo?

So the meaning depends on context and punctuation.

Because γιατί introduces a subordinate clause giving the reason:

• Αγόρασα ... , γιατί ...
• I bought ... , because ...

This is very natural punctuation in Greek. It works much like a comma before because in some English sentence structures.

και τα δύο means both or more literally the two as well / both of the two.

Breakdown:

• και = also, even, and
• τα δύο = the two

Together, και τα δύο is a very common Greek expression meaning both.

Examples:

• Μου αρέσουν και τα δύο. = I like both.
• Και τα δύο είχαν τελειώσει. = Both had run out.

Because τα δύο here is the normal neuter plural form used in the expression και τα δύο = both.

Even when the two things are nouns of different genders, Greek commonly uses this neuter plural expression to refer to them together as a set.

So although:

• σαμπουάν is neuter
• οδοντόκρεμα is feminine

Greek still says:

• και τα δύο = both

This is very common and natural.

είχαν τελειώσει is the pluperfect and means had finished / had run out.

Breakdown:

• είχαν = they had
• τελειώσει = finished

Together:

• είχαν τελειώσει = they had finished / they had run out

In this sentence, it means the shampoo and toothpaste were already finished before the speaker bought more.

So the sequence is:

1. The two items ran out.
2. Then the speaker bought more.

That is why the pluperfect makes sense.

Because it refers to two things: the shampoo and the toothpaste.

So Greek uses plural:

• είχαν = they had

Even though the two nouns have different genders, together they form a plural idea: both items.

Yes. Literally, τελειώνω means finish or come to an end, but with products or supplies it often means:

• be finished
• be used up
• run out

So:

• Η οδοντόκρεμα τελείωσε. = The toothpaste ran out.
• Το σαμπουάν τελείωσε. = The shampoo ran out.

In the sentence, και τα δύο είχαν τελειώσει means both products had been used up.

In this tense, the form τελειώσει stays the same. The number is shown by the auxiliary verb:

• είχα τελειώσει = I had finished
• είχες τελειώσει = you had finished
• είχε τελειώσει = he/she/it had finished
• είχαμε τελειώσει = we had finished
• είχατε τελειώσει = you had finished
• είχαν τελειώσει = they had finished

So the plural is marked by είχαν, not by changing τελειώσει.

Yes. επειδή can also mean because.

So you could say:

• Αγόρασα σαμπουάν και οδοντόκρεμα από το σούπερ μάρκετ, επειδή και τα δύο είχαν τελειώσει.

That is also correct. In everyday speech, γιατί is extremely common and natural.

Not completely. Greek word order is more flexible than English, though some orders sound more natural than others.

The given sentence is very natural:

• Αγόρασα σαμπουάν και οδοντόκρεμα από το σούπερ μάρκετ, γιατί και τα δύο είχαν τελειώσει.

You could move parts around for emphasis, for example:

• Από το σούπερ μάρκετ αγόρασα σαμπουάν και οδοντόκρεμα...

That would emphasize from the supermarket.

So the original order is standard, but not the only possible one.