Я оставил коробку внизу.

In the past tense, Russian verbs agree with the speaker’s gender in the singular.

• оставил = I left if the speaker is male
• оставила = I left if the speaker is female

So:

• Я оставил коробку внизу. = said by a man
• Я оставила коробку внизу. = said by a woman

This is one of the first things English speakers notice, since English past tense does not show the speaker’s gender.

Because коробка is the direct object of the verb оставить (to leave), and direct objects often go into the accusative case.

• dictionary form: коробка = box
• accusative singular: коробку

So:

• Я оставил коробку = I left the box

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

• книга → книгу
• машина → машину
• коробка → коробку

Внизу is an adverb meaning something like:

• down below
• at the bottom
• downstairs
  (depending on context)

In this sentence, Я оставил коробку внизу, it most naturally means:

• I left the box downstairs or
• I left the box down below

It refers to a location, but it does not name a specific noun like in the basement or on the ground floor. It is more general.

This is a very common question.

• внизу = down below / downstairs → location
• вниз = down(ward) → direction

Compare:

• Коробка внизу. = The box is downstairs / below.
• Я несу коробку вниз. = I’m carrying the box downstairs / downward.

In your sentence, the box is already in that place, so внизу is the right word.

Russian has no articles like a or the.

So коробку can mean:

• a box
• the box

The exact meaning depends on context.

In your sentence, if the meaning shown to the learner is I left the box downstairs, that comes from context, not from a separate word like the.

Yes. Russian often drops subject pronouns when the meaning is clear.

So both of these are possible:

• Я оставил коробку внизу.
• Оставил коробку внизу.

The second one still means I left the box downstairs, especially in conversation, because оставил already shows past singular masculine, which helps identify the speaker.

However, Я may be included for clarity, contrast, or emphasis.

Yes, but the meaning changes.

• оставил = perfective
  Focuses on the completed action: I left / I have left
• оставлял = imperfective
  Focuses more on the process, repetition, or background context: I was leaving / I used to leave / I had left (in some contexts)

In a simple statement about a completed act, оставил is the natural choice:

• Я оставил коробку внизу. = I left the box downstairs.

If you say:

• Я оставлял коробку внизу.

it may sound like:

• I used to leave the box downstairs
• I had left the box downstairs
• or it may need more context

So for a one-time completed action, оставил is usually best.

Yes. Russian word order is more flexible than English, because case endings carry a lot of the grammatical information.

The neutral order here is:

• Я оставил коробку внизу.

But you could also say:

• Коробку я оставил внизу.
  Emphasizes the box
• Внизу я оставил коробку.
  Emphasizes downstairs
• Я внизу оставил коробку.
  Also possible, with slightly different focus

The basic meaning stays similar, but the emphasis changes.

Not always. English leave has several meanings, and Russian uses different verbs depending on which meaning you want.

In this sentence, оставить means to leave something somewhere:

• Я оставил коробку внизу. = I left the box downstairs.

But other meanings of leave use other verbs, for example:

• leave a place → уйти / уехать / покинуть
• leave someone alone → оставить в покое
• leave for Moscow → уехать в Москву

So оставить is correct here because the meaning is put/keep something somewhere and go away.

It is pronounced roughly like vnee-ZOO.

A more detailed guide:

• в = like v
• ни = like nee
• зу = like zoo

Stress falls on the last syllable:

• внизу́

Also remember that unstressed vowels in Russian are often reduced in actual speech, so the real pronunciation may sound a little less neat than the spelling suggests.

Because внизу can work by itself as an adverb.

So:

• Я оставил коробку внизу. = I left the box downstairs / down below.

If you want to be more specific, you can add more words:

• внизу дома = at the bottom of the house/building
• внизу лестницы = at the bottom of the stairs
• внизу страницы = at the bottom of the page

But the single word внизу is already complete and natural on its own.