Я положил письмо в конверт и написал адрес очень аккуратно.

Положил is the past tense of положить, a perfective verb meaning to put / to place as a completed action.

In this sentence, the speaker is describing two finished actions:

• положил письмо в конверт = put the letter into the envelope
• написал адрес = wrote the address

A learner might compare this with класть / положить:

• класть = imperfective, focuses on the process or repeated action
• положить = perfective, focuses on the completed result

So Я положил письмо... means I put the letter... with the sense that the action was completed.

Поставил would usually be used for something set upright or placed in position, not naturally for a letter into an envelope.

That is the normal marker for the past tense in Russian.

The infinitive is положить. In the past tense:

• положил = masculine singular
• положила = feminine singular
• положило = neuter singular
• положили = plural

So Я положил tells us that the speaker is male. If the speaker were female, it would be:

Я положила письмо в конверт и написала адрес очень аккуратно.

Письмо is in the accusative case because it is the direct object of положил.

However, for many inanimate nouns, the accusative form is the same as the nominative form.
Since письмо is:

• neuter
• singular
• inanimate

its accusative is also письмо.

So:

• nominative: письмо
• accusative: письмо

That is why the form does not visibly change.

This is a very important Russian pattern.

With в, Russian uses:

• accusative for motion into something
• prepositional for location inside something

So:

• в конверт = into the envelope
• в конверте = in the envelope

Here the letter is being moved into the envelope, so Russian uses the accusative:

• Я положил письмо в конверт.

Compare:

• Письмо лежит в конверте. = The letter is in the envelope.

Because конверт is a masculine inanimate noun, and in the singular its accusative is the same as the nominative.

So:

• nominative: конверт
• accusative: конверт

This is similar to адрес later in the sentence:

• nominative: адрес
• accusative: адрес

If the noun were animate, the accusative would often look different.

Yes. Написал адрес literally means wrote the address.

In context, it usually means the person wrote the address on the envelope. Russian often leaves that part unstated if it is obvious from the situation.

Like положил, написал is also perfective, so it presents the action as completed:

• писал = was writing / wrote (process, repeated, or ongoing depending on context)
• написал = wrote, finished writing

So написал адрес emphasizes that the address was successfully written.

Because the sentence needs an adverb, not an adjective.

• аккуратный = neat, careful, tidy (adjective; describes a noun)
• аккуратно = neatly, carefully (adverb; describes a verb)

Here it describes how the person wrote the address:

• написал адрес очень аккуратно = wrote the address very neatly/carefully

So the adverb аккуратно is the correct form.

It can suggest both, depending on context.

Аккуратно often has a broader meaning than a single English word. It can mean:

• neatly
• carefully
• tidily
• with care

In this sentence, because it is about writing an address, the most natural English ideas are:

• very neatly
• very carefully

The exact nuance depends on what the speaker wants to stress:

• legible handwriting
• careful presentation
• precision

Yes, it could be omitted in many contexts.

Russian often leaves out personal pronouns when the subject is clear from the verb form or from context.

So both are possible:

• Я положил письмо в конверт и написал адрес очень аккуратно.
• Положил письмо в конверт и написал адрес очень аккуратно.

Including Я can:

• make the subject explicit
• add emphasis or contrast
• sound more natural if the sentence starts a new idea

Because положил and написал are masculine singular past forms, they do not by themselves show person, only gender and number. So context often helps.

Because the sentence describes a sequence of completed actions.

The person:

1. put the letter into the envelope
2. wrote the address

Both are presented as finished events, so perfective verbs are natural:

• положил
• написал

If you used imperfective forms, the meaning would shift toward process, background, repetition, or incomplete action:

• Я клал письмо в конверт и писал адрес... sounds like describing what you were doing, not simply stating two completed steps.

The word order is fairly natural, but Russian word order is more flexible than English.

The given version is neutral and straightforward:

• Я положил письмо в конверт и написал адрес очень аккуратно.

Other orders are possible, but they may change emphasis. For example:

• Я очень аккуратно написал адрес и положил письмо в конверт.
  This changes the sequence and puts more focus on очень аккуратно.
• Письмо я положил в конверт и адрес написал очень аккуратно.
  This sounds more contrastive or emphatic.

So the original order is probably the best basic version for a learner.

No. Russian has no articles like a or the.

So:

• письмо can mean a letter or the letter
• конверт can mean an envelope or the envelope
• адрес can mean an address or the address

The intended meaning comes from context.

In this sentence, English would usually use the because the situation is specific:

• I put the letter in the envelope and wrote the address very neatly.

Адрес is in the accusative case because it is the direct object of написал.

But like many masculine inanimate nouns, its accusative singular is the same as its nominative singular:

• nominative: адрес
• accusative: адрес

So again, the case is determined by function in the sentence, not by a visible ending change.

Not exactly as a single verb, but that is close to the practical meaning.

Russian says literally:

• put the letter into the envelope
• wrote the address

In context, that often corresponds to the real-world action of preparing a letter for mailing. English might sometimes summarize that as I addressed the envelope, but the Russian sentence is more explicit about the individual steps.

So the literal structure matters:

• написал адрес = wrote the address not
• a single verb meaning addressed

Because Russian often omits information that is obvious from context.

If you put a letter into an envelope and then write the address, it is naturally understood that the address is written on the envelope.

If needed, Russian could make it explicit:

• Я положил письмо в конверт и написал на нём адрес очень аккуратно.
• Я положил письмо в конверт и очень аккуратно написал адрес на конверте.

But in many situations, that would be unnecessary because the context already makes it clear.

The past-tense verbs would change to feminine forms:

Я положила письмо в конверт и написала адрес очень аккуратно.

Only the verbs change here:

• положил → положила
• написал → написала

The nouns and adverb stay the same.

Here и is just the normal conjunction and.

It connects two actions in sequence:

• put the letter into the envelope
• wrote the address

Russian does not need a special word to show that the second action happened after the first; the order of the verbs usually makes that clear.

So in this sentence, и is straightforward:

• ...в конверт и написал адрес... = ...into the envelope and wrote the address...