Możemy głosować nad zaliczką, która pokryje wydatki.

Because Polish usually builds the subject into the verb ending.

• możemy = we can / we may
• It comes from móc = to be able to / can

So Polish often does not need an explicit pronoun like my (we), unless you want emphasis or contrast.

• Możemy głosować... = We can vote...
• My możemy głosować... = We can vote... (with extra emphasis)

It most naturally means can or are able to here.

Polish móc can cover several English ideas:

• can = possibility/ability
• may = permission, in some contexts
• be able to = ability

In this sentence, możemy głosować most likely means we can vote or we are able to vote, depending on context.

This is about aspect, which is very important in Polish.

• głosować is imperfective
• zagłosować is perfective

Here, głosować focuses on the activity/process of voting: we can vote on...

A rough contrast:

• Możemy głosować nad zaliczką. = We can vote on the advance.
• Możemy zagłosować nad zaliczką. = We can cast a vote / vote once on the advance.

Both can be possible depending on context, but głosować is very natural when talking generally about holding a vote or voting on a matter.

With głosować, Polish often uses nad + instrumental to mean to vote on / over something.

So:

• głosować nad projektem = vote on the proposal
• głosować nad ustawą = vote on the bill
• głosować nad zaliczką = vote on the advance

You should learn this as a common pattern:

• głosować nad + instrumental

Because the preposition nad requires the instrumental case here.

Base form:

• zaliczka = advance / deposit / prepayment

Instrumental singular:

• zaliczką

So:

• nad zaliczką = on/about the advance

This is a standard feminine noun pattern:

• nominative: zaliczka
• instrumental: zaliczką

Zaliczka usually means an advance payment, deposit, or prepayment.

The exact English translation depends on context:

• in business: advance payment
• when reserving something: deposit
• in budgeting/accounting: advance

In this sentence, it sounds like some kind of advance sum of money that will cover expenses.

Która means which or that, and it refers back to zaliczką.

Since zaliczka is:

• feminine
• singular

the relative pronoun must match it:

• który = masculine
• która = feminine
• które = neuter

So:

• zaliczka, która... = the advance, which/that...

Even though zaliczką is in the instrumental case after nad, the pronoun która is nominative here because it is the subject of pokryje.

Because in the clause która pokryje wydatki, the pronoun is the subject of the verb.

Compare:

• która pokryje wydatki = which will cover the expenses
  • here która is doing the action, so it is nominative

But if it were the object, you would use którą:

• zaliczka, którą zatwierdzimy = the advance that we will approve
  • here którą is the object of zatwierdzimy

So the form depends on the role inside the relative clause, not on the case of zaliczką before it.

It looks like a present-tense form, but because pokryć is a perfective verb, pokryje has future meaning.

• pokrywać = imperfective = to be covering / to cover in an ongoing or repeated sense
• pokryć = perfective = to cover completely, to cover once, to cover successfully

So:

• pokryje wydatki = will cover the expenses

This is a very common Polish pattern: perfective verbs use present-looking forms to express the simple future.

Yes, but the meaning would shift.

• pokryje wydatki = will cover the expenses
  Focus: the result will be achieved.

• będzie pokrywać wydatki = will be covering the expenses
  Focus: the process or ongoing action.

In this sentence, pokryje is more natural because the idea is that the advance will be enough to cover the expenses.

Here wydatki is in the accusative plural, because it is the object of pokryje.

Base form:

• wydatek = expense
• plural: wydatki = expenses

For many inanimate masculine nouns in Polish, the accusative plural looks the same as the nominative plural. That is why wydatki does not visibly change here.

Because Polish normally puts a comma before a relative clause introduced by words like:

• który / która / które
• że
• bo
• gdy
• jeśli

So:

• zaliczką, która pokryje wydatki

This is standard Polish punctuation. In English, relative clauses are punctuated differently depending on meaning, but in Polish the comma here is normal.

Yes, Polish word order is fairly flexible, though some orders sound more natural than others.

The original sentence is natural and neutral:

• Możemy głosować nad zaliczką, która pokryje wydatki.

Possible variations can shift emphasis:

• Nad zaliczką, która pokryje wydatki, możemy głosować.
• Możemy nad zaliczką głosować, która pokryje wydatki.
  This one sounds less natural.

In general, the original version is the best choice for normal usage.

A rough pronunciation guide:

• Możemy ≈ mo-ZHEH-mi
• głosować ≈ gwo-SO-vach
• nad zaliczką ≈ nad za-LEECH-kaw
• która ≈ KTOO-ra
• pokryje ≈ po-KRI-yeh
• wydatki ≈ vih-DAT-kee

A few helpful sounds:

• ż sounds like the s in measure
• ł sounds like English w
• cz / ć / ci and similar letters are softer or harder ch-type sounds
• ą is a nasal vowel; at the end of a word it is often pronounced somewhat like -om / -aw depending on context

Either can work in English, depending on style.

• zaliczką, która pokryje wydatki
  = the advance, which will cover the expenses = the advance that will cover the expenses

In Polish, która is the normal relative pronoun here. English may choose which or that depending on nuance and style, but Polish does not make exactly the same distinction as English does.