В бухгалтерии мне объяснили, когда придёт аванс и где взять копию квитанции.

Because here в means in / at a place, not into a place.

• в бухгалтерии = in the accounting department / at the accounting office
• This uses the prepositional case after в for location.
• бухгалтерия is the dictionary form.
• Prepositional singular: в бухгалтерии

Compare:

• Я работаю в бухгалтерии. = I work in accounting.
• Я иду в бухгалтерию. = I am going to the accounting office.

So in your sentence, the speaker is already there or is referring to that location, so в бухгалтерии is correct.

In this sentence, бухгалтерия usually means the accounting department, payroll, or the accounting office in a company or institution.

So В бухгалтерии мне объяснили... is very natural Russian for:

• In accounting, they explained to me...
• At the accounting office, they explained to me...

It does not usually mean the abstract subject accounting here. It means the department or office.

Because объяснить / объяснять usually takes:

• the thing explained
• and the person to whom it is explained in the dative

So:

• мне объяснили = they explained to me

Examples:

• Мне объяснили правило. = They explained the rule to me.
• Ему объяснили, что делать. = They explained to him what to do.

So мне is the indirect object: to me.

This is a very common Russian pattern.

Объяснили is:

• past tense
• plural
• perfective

Russian often uses a 3rd person plural verb with no subject when the specific people are unknown, unimportant, or obvious from context.

So:

• Мне объяснили literally = They explained to me
• but in English we often translate it more naturally as I was told or they explained to me

The idea is something like the people there explained it to me.

Other examples:

• Мне сказали подождать. = They told me to wait.
• Меня попросили прийти завтра. = They asked me to come tomorrow.

Because объяснили is perfective, and it presents the explanation as a completed event.

• объяснили = they explained / they finished explaining
• объясняли = they were explaining / used to explain / explained repeatedly

In this sentence, the speaker means that they received the needed explanation as a completed piece of information, so объяснили is the natural choice.

Compare:

• Мне объяснили, когда придёт аванс. = They explained to me when the advance will arrive.
• Мне долго объясняли, как это работает. = They were explaining to me for a long time how this works.

Because когда придёт аванс и где взять копию квитанции is a subordinate clause structure depending on объяснили.

Russian usually puts a comma before subordinate clauses introduced by words like:

• что = that
• когда = when
• где = where
• почему = why
• как = how

So:

• мне объяснили, когда придёт аванс...

The comma marks the start of what was explained.

Because both parts belong to the same main verb объяснили and are joined by и.

Structure:

• мне объяснили, [когда придёт аванс] и [где взять копию квитанции]

Both subordinate parts are parallel:

• when the advance will arrive
• where to get a copy of the receipt

Since they are coordinated with и, Russian normally uses one comma before the first subordinate part, not another one before где.

Because the clause refers to a future event: the advance payment has not arrived yet.

придёт is the future form of the perfective verb прийти.

• когда придёт аванс = when the advance comes / arrives

In Russian, perfective verbs form a simple future:

• прийти → придёт

This is natural when talking about a one-time completed arrival.

Because аванс here is expected as a single payment on a particular occasion, not as a repeated or ongoing process.

• придёт аванс = the advance payment will arrive / come in
• будет приходить would suggest repeated arrival or an ongoing pattern, which does not fit well here

Russian often uses motion or arrival verbs for money/payments in colloquial or workplace language:

• зарплата пришла = the salary came in
• деньги ещё не пришли = the money hasn’t come in yet

So когда придёт аванс sounds very natural.

In everyday Russian work/payroll context, аванс often means:

• an advance payment
• especially a salary advance paid before the main paycheck

So it may not just mean any abstract advance in general. In office/payroll language, it often refers to the first part of a monthly wage.

Russian very often uses a question word + infinitive construction when talking about instructions or practical information.

So:

• где взять копию квитанции = where to get a copy of the receipt
• more literally: where [one/I can] get a copy of the receipt

The subject is left unstated because it is understood from context.

This is extremely common:

• что делать? = what to do?
• куда пойти? = where to go?
• где купить билеты? = where to buy tickets?

You could say где я могу взять копию квитанции, but где взять копию квитанции is shorter and very natural.

Usually it is understood as the relevant person from context, often:

• I
• one
• we
• or the person asking

In this sentence, because of мне объяснили, the natural understanding is:

• they explained to me where I could get a copy of the receipt

Russian often leaves this kind of subject implicit in infinitive constructions.

Because копию is the accusative singular of копия, and it is the direct object of взять.

• dictionary form: копия
• accusative singular: копию

So:

• взять копию = to take/get a copy

This is a regular pattern for many feminine nouns ending in -ия:

• лекция → лекцию
• компания → компанию
• квитанция → квитанцию

Because Russian expresses copy of the receipt with:

• копия чего? = copy of what?
• so the second noun goes into the genitive

Therefore:

• копия квитанции = a copy of the receipt
• взять копию квитанции = to get a copy of the receipt

Cases here:

• копию = accusative, because it is the thing being taken
• квитанции = genitive, because it depends on копия

This is the same pattern as:

• часть книги = part of the book
• конец фильма = the end of the film
• номер телефона = phone number

Often yes, but the exact meaning depends on context.

Квитанция can mean:

• a receipt
• a payment slip
• a proof-of-payment document

In office or bureaucratic settings, it often refers to an official paper showing that something was paid or processed.

So копия квитанции is naturally a copy of the receipt or a copy of the payment receipt/document.

Yes, Russian word order is flexible.

This order puts the setting first:

• В бухгалтерии = in the accounting department

Then:

• мне = to me
• объяснили = explained

So the sentence begins by setting the scene: At the accounting office...

Other possible orders include:

• Мне в бухгалтерии объяснили...
• Объяснили мне в бухгалтерии...

These are all possible, but they differ slightly in emphasis. The original version sounds very natural and neutral.

Grammatically, yes, but it sounds less natural in English.

A more natural English rendering would usually be something like:

• At the accounting office, they explained to me when the advance would arrive and where to get a copy of the receipt.
• In accounting, they told me when the advance would come in and where to get a copy of the receipt.

The Russian structure is straightforward, but English usually prefers:

• would arrive instead of will come in reported contexts
• get rather than take for взять in this sentence

Here взять is best understood as get / obtain / pick up.

Although взять often literally means to take, in many contexts it is broader:

• Где взять справку? = Where can I get a certificate?
• Где взять бланк? = Where can I get a form?
• Где взять копию квитанции? = Where can I get a copy of the receipt?

So in this sentence, get is usually the best English choice.