Η μαξιλαροθήκη είναι πάνω στο κομοδίνο, δίπλα στο βιβλίο που διάβαζα χτες.

Η is the feminine singular definite article, meaning the.

μαξιλαροθήκη is a feminine noun, so it takes η in the nominative singular:

• η μαξιλαροθήκη = the pillowcase

It is in the nominative because it is the subject of the sentence — the thing that is somewhere.

στο is a contraction of σε + το.

• σε = in / at / on / to, depending on context
• το = the for a neuter singular noun

So:

• στο κομοδίνο = on the bedside table / on the nightstand
• literally, σε το κομοδίνο, but Greek normally contracts this to στο

The same thing happens in:

• δίπλα στο βιβλίο = next to the book

Because both nouns are neuter singular.

• το κομοδίνο = the bedside table / nightstand
• το βιβλίο = the book

In Greek, nouns have grammatical gender, and the article has to match the noun:

• masculine: ο
• feminine: η
• neuter: το

πάνω στο means on or more literally on top of.

In this sentence:

• πάνω στο κομοδίνο = on the bedside table

Greek often expresses location with combinations like:

• πάνω σε / πάνω στο = on
• κάτω από = under
• δίπλα σε / δίπλα στο = next to

So πάνω gives the idea of position above/on top, and στο κομοδίνο tells you what it is on.

In this sentence, the noun after them is in the accusative:

• στο κομοδίνο
• στο βιβλίο

That is because these expressions are built with σε:

• πάνω σε
• δίπλα σε

And σε normally takes the accusative in Modern Greek.

For neuter singular nouns like κομοδίνο and βιβλίο, the nominative and accusative forms look the same, so you do not see a change in the noun itself. You mainly notice it in the article:

• το can be nominative or accusative for neuter singular

The comma separates two location phrases:

• πάνω στο κομοδίνο
• δίπλα στο βιβλίο που διάβαζα χτες

It helps the sentence read more clearly:

• the pillowcase is on the bedside table
• and it is next to the book I was reading yesterday

In everyday Greek, the comma may sometimes be omitted in similar sentences, but here it helps organize the information.

που is the relative word meaning that / which / who in many contexts.

So:

• το βιβλίο που διάβαζα χτες = the book that I was reading yesterday

It connects the book with the clause describing it.

Greek που is very common and much simpler than English in some ways because it does not change form for gender or number here. It can refer to:

• people
• things
• singular or plural nouns

διάβαζα is the imperfect past form, which often suggests:

• an ongoing action in the past
• a repeated/habitual action in the past
• background description

So here:

• το βιβλίο που διάβαζα χτες = the book I was reading yesterday

If the sentence used διάβασα, that would be the simple past (aorist) and would mean more like:

• the book I read yesterday

So the difference is roughly:

• διάβαζα = was reading
• διάβασα = read

Yes. Even though χτες means yesterday, the imperfect is still possible because it can describe what was in progress during that time.

So:

• που διάβαζα χτες = that I was reading yesterday

This sounds natural if the speaker is thinking of the book as something they were engaged with yesterday, not necessarily something they finished.

If the focus were on completing the book yesterday, Greek would more likely use διάβασα instead.

Yes. χτες and χθες both mean yesterday.

• χτες is very common in everyday speech and writing
• χθες is a more conservative or formal spelling/form

Both are correct. A learner will hear χτες very often in conversation.

Greek word order is fairly flexible, and time expressions like χτες can often move around.

Here, putting χτες at the end is very natural:

• το βιβλίο που διάβαζα χτες

It keeps χτες close to the verb διάβαζα, which it modifies.

You could also hear:

• το βιβλίο που χτες διάβαζα

But that sounds more marked or stylistically different. The version in your sentence is the most natural everyday order.

It describes the location of the pillowcase.

The structure is:

• Η μαξιλαροθήκη είναι πάνω στο κομοδίνο = the pillowcase is on the bedside table
• δίπλα στο βιβλίο που διάβαζα χτες = next to the book I was reading yesterday

So the book is not being described as next to something else. Rather, the pillowcase is being located relative to the book.

Yes, but the meaning and style would shift slightly.

• είναι = is
• βρίσκεται = is located / is situated / can be found

So:

• Η μαξιλαροθήκη είναι πάνω στο κομοδίνο is the most straightforward everyday way to say it.
• Η μαξιλαροθήκη βρίσκεται πάνω στο κομοδίνο sounds a little more formal or descriptive.

In ordinary conversation, είναι is the most natural choice here.