Όταν ακούω την κόρνα, κοιτάω από το παράθυρο.

Όταν means when. In this sentence, it has the sense of whenever or every time that because both actions are in the present and describe something habitual:

• Όταν ακούω την κόρνα, κοιτάω από το παράθυρο.
• Whenever I hear the horn, I look out the window.

So it is not just one single event; it sounds like a repeated pattern.

Greek often leaves out subject pronouns because the verb ending already shows who the subject is.

Here:

• ακούω = I hear
• κοιτάω = I look

So Greek does not need εγώ unless you want emphasis or contrast.

For example:

• Εγώ ακούω την κόρνα, όχι αυτός. = I hear the horn, not him.

In your sentence, leaving out εγώ is completely normal.

They are in the present tense because the sentence describes a regular or repeated action:

• When/Whenever I hear the horn, I look out the window.

This is very similar to English, which also often uses the present in sentences about habits.

So:

• ακούω = I hear / I am hearing
• κοιτάω = I look / I am looking

But here the overall meaning is habitual, not necessarily happening right this second.

την κόρνα literally means the horn.

In everyday Greek, κόρνα usually means a car horn, and very often it can refer not just to the object itself but to the sound of the horn or a honk.

So in this sentence, a learner might naturally understand it as:

• the horn
• or more naturally in English, the honk / the sound of the horn

Greek often uses the noun this way where English might choose a slightly different expression.

Because κόρνα is the direct object of ακούω (I hear), it must be in the accusative case.

The forms are:

• η κόρνα = the horn (nominative, used for the subject)
• την κόρνα = the horn (accusative, used for the direct object)

Compare:

• Η κόρνα ακούγεται δυνατά. = The horn sounds loud.
  Here η κόρνα is the subject.

• Ακούω την κόρνα. = I hear the horn.
  Here την κόρνα is the object.

Greek uses the definite article very often, sometimes more often than English does.

So Greek may say:

• την κόρνα = literally the horn
• το παράθυρο = the window

Even if English might sometimes say a horn, the horn, or simply phrase it differently, Greek often prefers the article when the thing is understood from context.

In this sentence:

• την κόρνα suggests a familiar or contextually identifiable horn sound
• το παράθυρο suggests the window that is relevant in the situation, often the window in the room/house

Because κοιτάω means look, while βλέπω means see.

This is the difference:

• κοιτάω = direct your eyes/attention somewhere
• βλέπω = see, perceive with your eyes

So:

• κοιτάω από το παράθυρο = I look out the window
• βλέπω από το παράθυρο would sound different and would focus more on what you can see, not on the act of turning your attention there

In your sentence, the idea is that when the person hears the horn, they intentionally go and look.

Literally, από το παράθυρο means from the window, but in this kind of sentence it is understood more naturally as:

• out of the window
• through the window
• out the window

So:

• κοιτάω από το παράθυρο = I look out of / through the window

This is a good example of how Greek από can cover meanings that English expresses with different prepositions.

Also compare:

• κοιτάω το παράθυρο = I look at the window
• κοιτάω από το παράθυρο = I look out of / through the window

That is an important difference.

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

Your sentence is very natural:

• Όταν ακούω την κόρνα, κοιτάω από το παράθυρο.

But you could also say:

• Κοιτάω από το παράθυρο όταν ακούω την κόρνα.

Both are grammatical. The version with Όταν... first is often preferred when you want to set the time or condition first: When I hear the horn...

So the original order is a very natural, neutral choice.

Yes. κοιτάω and κοιτάζω are both standard forms.

So both of these are correct:

• κοιτάω από το παράθυρο
• κοιτάζω από το παράθυρο

They mean the same thing. Which one you hear more often can depend on speaker preference, region, and style.

Similarly, you may see pairs like this with other verbs in Modern Greek. It is normal.

Because Όταν ακούω την κόρνα is a subordinate clause placed before the main clause.

So the structure is:

• Όταν ακούω την κόρνα, = subordinate time clause
• κοιτάω από το παράθυρο. = main clause

Greek commonly uses a comma here, just as English usually does when a when clause comes first:

• When I hear the horn, I look out the window.

So the comma is normal and helps separate the two parts clearly.