Το φίδι κρύβεται κάτω από την πέτρα.

Because Greek articles change to match the noun’s gender, number, and case.

• το φίδι = the snake
• την πέτρα = the stone / the rock

Here:

• το is the neuter singular form
• την is the feminine singular accusative form

So Greek does not use just one word for the the way English does.

Φίδι is neuter.

That is why it takes the article το:

• το φίδι = the snake

Its basic form is already φίδι. Many Greek neuter nouns often use το in the singular nominative and accusative.

Because after the preposition από, Greek uses the accusative case.

So:

• η πέτρα = the stone as the subject form (nominative)
• την πέτρα = the stone after a preposition like από (accusative)

In this sentence, πέτρα is not the subject. It is the object of the prepositional phrase κάτω από την πέτρα = under the stone.

The dictionary form is κρύβομαι.

κρύβεται is the 3rd person singular present form, so it means:

• he/she/it hides
• he/she/it is hiding

Since the subject is το φίδι, here it means the snake hides / is hiding.

Greek has a set of verb endings often called middle/passive endings. Κρύβεται uses that set.

But in meaning, it does not have to be a true passive in English. Here it means something like:

• it hides
• it is hiding
• very literally, it hides itself

So although the form may look passive to a learner, the natural English meaning here is active: The snake is hiding under the stone.

In this sentence, the most natural meaning is is hiding.

Greek present tense often covers both:

• simple present: hides
• present progressive: is hiding

So Το φίδι κρύβεται κάτω από την πέτρα can be understood as:

• The snake hides under the stone
• The snake is hiding under the stone

In normal English, is hiding is usually the best translation here.

Greek commonly expresses under/below with the combination κάτω από.

• κάτω = down / below
• από = from, but in this expression it helps form the meaning under / beneath

So:

• κάτω από την πέτρα = under the stone

This is a very common pattern in Greek. You should learn κάτω από as a unit meaning under / beneath.

Από takes the accusative in Modern Greek.

That is why you get:

• την πέτρα not
• η πέτρα

Other examples:

• από το σπίτι = from the house
• από τον φίλο = from the friend
• από την πόλη = from the city

In your sentence, κάτω από την πέτρα still follows that same rule.

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

The neutral order here is:

• Το φίδι κρύβεται κάτω από την πέτρα.

But you could also hear:

• Κάτω από την πέτρα κρύβεται το φίδι.

That version puts more emphasis on under the stone or sounds a bit more dramatic. The meaning stays basically the same.

A rough pronunciation is:

to FEE-thee KREE-ve-te KAH-to a-PO teen PEH-tra

A few helpful notes:

• φ sounds like f
• δ in φίδι sounds like the th in this
• κρύβεται is stressed on κρύ-
• πέτρα is stressed on πέ-
• την is often pronounced tin in everyday speech before consonants, even though it is written την

So the sentence flows roughly like:

to FEE-thee KREE-ve-te KAH-to a-PO tin PEH-tra

Yes, but it means something slightly different.

• Το φίδι κρύβεται κάτω από την πέτρα = The snake is hiding under the stone
• Το φίδι είναι κάτω από την πέτρα = The snake is under the stone

The first sentence emphasizes the idea of hiding. The second simply states the snake’s location.

So both are correct, but they are not exactly the same in meaning.