Я считаю расходы в приложении.

Считаю is the 1st person singular form of считать.

So:

• я считаю = I count / I am counting / I keep track of

Because Russian present-tense forms often cover both simple present and present continuous, this can mean either:

• I count expenses in the app
• I’m counting expenses in the app
• I track expenses in the app

Context tells you which one is meant.

Yes, it does. Считать has more than one common meaning.

For example:

• Я считаю расходы = I count expenses
• Я считаю, что это правильно = I think that this is correct
• Я считаю его умным = I consider him smart

So how do you know which meaning it has?
You look at the context and the object:

• with numbers, money, items, totals, etc. → count
• with a clause or opinion → think / consider

In your sentence, расходы means expenses, so считаю is understood as count / total up / track.

Because Russian often uses расходы in the plural for expenses as a general category, just like English often says expenses rather than expense.

• расходы = expenses
• расход = an expense, expenditure, consumption, outlay

In personal finance or budgeting, расходы is very common and natural.

Расходы is in the accusative case because it is the direct object of считаю.

You are counting what?
→ расходы

But for inanimate plural nouns, the accusative looks exactly like the nominative.

So:

• nominative plural: расходы
• accusative plural: расходы

That is why the form does not look different here.

Because в can take different cases depending on the meaning.

Here it means location: in the app.
With location, в normally takes the prepositional case.

• приложение = app / application
• в приложении = in the app

If you were talking about motion into something, Russian would use the accusative instead.

So:

• в приложении = in the app
• в приложение = into the app

In your sentence, the idea is location, so в приложении is correct.

It is the prepositional singular form of приложение.

The pattern is:

• nominative: приложение
• prepositional: в приложении

This is very common after в when you mean in a place or environment.

Yes. Приложение can mean:

• app / application
• appendix
• attachment or enclosure, depending on context

So в приложении could sometimes mean:

• in the app
• in the attachment
• in the appendix

Usually the wider context makes it clear. In modern everyday speech, especially about phones or finance, people will often understand приложение as app.

You can often drop it.

Russian verbs usually show the subject clearly, and считаю already means I count. So all of these are possible:

• Я считаю расходы в приложении.
• Считаю расходы в приложении.

Including я can sound:

• more neutral in isolation
• more emphatic
• clearer in contrast with someone else

For example:

• Я считаю расходы в приложении, а он — в таблице.
  I track expenses in an app, and he does it in a spreadsheet.

It can be either.

Russian imperfective present often covers both:

• a habit / regular activity
• an action happening right now

So this sentence could mean:

• I track my expenses in an app
• I’m counting my expenses in the app

Context tells you which one is intended.

Then Russian will often use a perfective verb.

Compare:

• Я считаю расходы в приложении.
  = I count / I’m counting / I track expenses in the app

• Я посчитал расходы в приложении.
  = I counted / I totaled up the expenses in the app

• Я посчитаю расходы в приложении.
  = I will count / total up the expenses in the app

So считать here is the imperfective partner, while посчитать is a common perfective partner.

It is understandable and can be natural, but it depends on the exact meaning you want.

If you literally mean I count / total up expenses, then Я считаю расходы в приложении works well.

If you mean I keep track of / log / monitor expenses, some speakers might prefer:

• Я веду учёт расходов в приложении. = I keep track of expenses in an app.
• Я отслеживаю расходы в приложении. = I monitor/track expenses in an app.
• Я записываю расходы в приложении. = I record expenses in an app.

So your sentence is good, but there are other natural options depending on nuance.

You can, but you do not have to.

• Я считаю расходы в приложении. = I count/track expenses in the app.
• Я считаю свои расходы в приложении. = I count/track my expenses in the app.

Adding свои makes it explicitly my own expenses. Without it, the sentence is still perfectly normal if the context already makes that obvious.

Yes. Russian word order is flexible, and changing it often changes the focus or emphasis, not the core meaning.

Examples:

• Я считаю расходы в приложении.
  Neutral order.

• В приложении я считаю расходы.
  Emphasis on in the app.

• Расходы я считаю в приложении.
  Emphasis on expenses.

So the original order is a good neutral choice, but other orders are also possible.

The main stresses are:

• я счита́ю расхо́ды в приложе́нии

A rough pronunciation guide:

• я = ya
• счита́ю = schi-TA-yu
• расхо́ды = ras-KHO-dy
• в приложе́нии = v pri-la-ZHE-ni-i

The stress matters in Russian, so it is good to learn the stressed syllables together with the word.