Το έγραψα λάθος.

Word by word:

• το = it
• έγραψα = I wrote
• λάθος = wrong / incorrectly / by mistake

So the whole sentence means something like I wrote it wrong or I wrote it incorrectly.

το is the direct object pronoun here, meaning it.

Greek often uses short object pronouns like:

• τον = him
• την = her
• το = it

So in Το έγραψα λάθος, the speaker is talking about some neuter singular thing already known from context, and says I wrote it wrong.

In normal Greek statements, these short object pronouns usually go before the finite verb.

So:

• Το έγραψα = I wrote it
• not usually Έγραψα το by itself

This is a very common Greek pattern. English puts it after the verb, but Greek usually puts το before it.

έγραψα is the aorist form of γράφω.

Here it means:

• I wrote
• I wrote it once / I completed the action

It is first person singular, so the subject is I.

Compare:

• γράφω = I write / I am writing
• έγραψα = I wrote

That έ- is called the augment, a common feature in past tenses in Greek.

In many verbs, especially in the aorist and imperfect, Greek adds this extra sound at the beginning in past forms:

• γράφω → έγραψα

It helps mark the verb as past.

The accent in έγραψα also shows where the stress falls: EH-gra-psa.

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

In έγραψα, the ending -α tells you it means I wrote.

So Greek does not need εγώ unless the speaker wants emphasis:

• Έγραψα λάθος = I wrote wrong
• Εγώ έγραψα λάθος = I wrote it wrong / I was the one who wrote it wrong

Yes, λάθος is very often a noun meaning mistake, but in Modern Greek it is also very commonly used in an adverbial way.

So:

• λάθος = wrongly / incorrectly / by mistake

That is very natural Greek.

So Το έγραψα λάθος literally looks like I wrote it mistake, but idiomatically it means I wrote it wrong.

Yes. Το έγραψα λανθασμένα is correct and means basically the same thing: I wrote it incorrectly.

But there is a difference in tone:

• λάθος = very common, everyday, natural
• λανθασμένα = more formal or more bookish

In ordinary conversation, λάθος is usually the more natural choice.

Yes, Greek word order is more flexible than English, but changing the order usually changes the emphasis.

Neutral order:

• Το έγραψα λάθος.

Possible emphatic order:

• Λάθος το έγραψα. = I wrote it wrong.
  This puts extra focus on wrong.

Another possible order:

• Το λάθος έγραψα.

But be careful: this can sound like I wrote the wrong thing or It was the wrong one that I wrote, so it is not the same neutral meaning as the original sentence.

In this sentence, λάθος describes the action of writing, not the object itself.

So it means:

• I wrote it incorrectly
• not It is wrong and I wrote it

That is why in English we usually translate it with an adverb-like expression such as wrong, incorrectly, or by mistake.

A simple pronunciation guide is:

To E-gra-psa LA-thos

More approximately:

• Το = to
• έγραψα = EH-gra-psa
• λάθος = LA-thos
  where th is like the th in think

The main stresses are on:

• έ in έγραψα
• λά in λάθος

Yes, depending on context, Το έγραψα λάθος can mean either:

• I wrote it wrong
• I wrote it incorrectly
• I wrote it by mistake

The exact English translation depends on what the speaker means in context. Greek λάθος can cover both incorrectly and by mistake.