Корректор исправил опечатку.

Because it is the direct object of the verb исправил (corrected / fixed), so it goes into the accusative case.

• Dictionary form: опечатка
• Accusative singular: опечатку

This is a very common pattern for feminine nouns ending in -а:

• ошибка → ошибку
• книга → книгу
• опечатка → опечатку

So Корректор исправил опечатку literally has the structure:

• Корректор = the proofreader/corrector
• исправил = corrected
• опечатку = the typo

Исправил is the past tense masculine singular form of исправить.

Russian past tense is built from the infinitive stem plus endings that agree with the subject’s gender and number:

• исправил = masculine singular
• исправила = feminine singular
• исправило = neuter singular
• исправили = plural

Since корректор is a masculine noun, the verb is исправил.

So:

• Корректор исправил опечатку.
• Корректорша исправила опечатку. (if using a feminine subject noun)

This is a question of aspect.

• исправить → perfective
• исправлять → imperfective

Исправил presents the action as completed: the typo got corrected.

So Корректор исправил опечатку means something like:

• The proofreader corrected the typo
• The typo was successfully fixed

If you said исправлял, the focus would be different. It would suggest:

• he was correcting it,
• he used to correct it,
• or the action is being viewed as a process rather than a completed result.

For a simple finished event, исправил is the natural choice.

Because корректор is the subject of the sentence, so it is in the nominative case, which is the dictionary form.

• корректор = nominative singular
• опечатку = accusative singular

Russian marks grammatical roles with cases much more than English does.

So in this sentence:

• Корректор = who did the action
• опечатку = what was affected by the action

That is why only опечатка changes form here.

Not exactly in normal English usage.

In this sentence, корректор usually means a proofreader or someone who corrects text, especially in publishing, editing, or printing contexts.

So while the word is related to correct, the best natural English equivalent is often:

• proofreader
• sometimes copy editor, depending on context

A learner might translate it literally as corrector, but that is usually not the most natural English word here.

Опечатка is more specific.

• опечатка = a typo, a typing/printing mistake
• ошибка = a more general mistake or error

So if someone accidentally types the wrong letter or leaves one out, that is an опечатка.

Examples:

• Я заметил опечатку в слове. = I noticed a typo in the word.
• Это была ошибка, а не опечатка. = It was a mistake, not a typo.

In your sentence, опечатку tells us the problem was specifically a typo, not just any kind of error.

Because Russian has no articles.

English needs words like:

• a
• an
• the

Russian does not use them. Whether something is a proofreader, the proofreader, a typo, or the typo is understood from context.

So Корректор исправил опечатку could be translated as:

• The proofreader corrected the typo
• A proofreader corrected a typo

The exact English choice depends on the situation, not on a separate Russian word.

Yes. Russian word order is more flexible than English because case endings show grammatical roles.

The neutral word order here is:

• Корректор исправил опечатку.

But you could also say:

• Опечатку исправил корректор.
• Исправил корректор опечатку.

These alternatives are grammatically possible, but they change the focus or emphasis.

For example:

• Корректор исправил опечатку. = neutral statement
• Опечатку исправил корректор. = emphasizes the typo
• Исправил корректор опечатку. = can sound more marked or stylistic

So yes, the order can change, but the default version is usually best for beginners.

A reasonable learner-friendly pronunciation guide is:

корре́ктор испра́вил опеча́тку

Approximate English-style pronunciation: kar-RYEK-tar ees-PRA-veel a-pa-CHAT-koo

A few useful notes:

• Unstressed о often sounds closer to a.
• Russian р is rolled or tapped.
• к and т are always hard, clear consonants.
• The stress matters a lot in Russian, so it helps to learn the stressed syllables early.

Sometimes, yes.

Russian often omits subjects when they are already clear from context. So in a suitable situation, someone could simply say:

• Исправил опечатку.

That would mean something like:

• He corrected the typo
• [Someone] corrected the typo

But without context, it is less clear than the full sentence.

In a standalone example for learners, Russian usually keeps the subject:

• Корректор исправил опечатку.

That makes the grammar easier to see.