Ich muss die Rechnung noch bezahlen, bevor wir gehen.

Because müssen is the infinitive form, while muss is the form for ich in the present tense.

• ich muss = I must / I have to
• du musst
• er/sie/es muss
• wir müssen
• ihr müsst
• sie/Sie müssen

So Ich muss is the correct conjugated form.

Because müssen is a modal verb, and in German modal verbs usually send the second verb to the end in its infinitive form.

So the pattern is:

• Ich muss bezahlen. = I have to pay.

In your sentence:

• Ich muss die Rechnung noch bezahlen

Here:

• muss is the conjugated modal verb in position 2
• bezahlen stays at the end of that clause as the infinitive

This is one of the most common German sentence patterns.

Because after a modal verb like müssen, German does not use zu.

Compare:

• Ich muss bezahlen. = I have to pay.
• Ich versuche zu bezahlen. = I’m trying to pay.

So:

• after müssen, können, wollen, sollen, dürfen, mögen → usually no zu
• after many other verbs → often zu + infinitive

That is why Ich muss die Rechnung noch bezahlen is correct, not Ich muss die Rechnung noch zu bezahlen.

Because Rechnung is a feminine noun:

• die Rechnung = the bill / invoice / check

And here it is the direct object of bezahlen, so it is in the accusative case. For feminine nouns, the article stays die in both nominative and accusative:

• nominative: die Rechnung
• accusative: die Rechnung

So you do not see a change, but it is still accusative in function.

In this sentence, die Rechnung most naturally means the bill or the check, especially in a restaurant or café context.

Depending on context, Rechnung can also mean:

• invoice
• bill
• calculation in math

So the sentence could mean:

• I still have to pay the bill before we leave or, in another context,
• I still have to pay the invoice before we leave

Here noch means something like still or yet.

So:

• Ich muss die Rechnung bezahlen = I have to pay the bill.
• Ich muss die Rechnung noch bezahlen = I still have to pay the bill / I have yet to pay the bill.

It adds the idea that this action has not happened yet, but needs to happen before something else.

In this sentence, noch suggests:

• paying the bill is one more thing that remains to be done

Because bevor is a subordinating conjunction, and subordinating conjunctions send the conjugated verb to the end of their clause.

So:

• wir gehen = we go / we leave

In the subordinate clause:

• bevor wir gehen = before we leave

This is normal German subordinate-clause word order:

• bevor
  • subject + ... + verb

If the clause were longer, the verb would still come at the end:

• bevor wir nach Hause gehen = before we go home

Because bevor wir gehen is a subordinate clause, not a main clause.

In a main clause, German usually puts the conjugated verb in position 2:

• Wir gehen jetzt.

But after bevor, the verb moves to the end:

• bevor wir gehen

So gehen wir would be the wrong word order here.

Yes. You can also say:

• Bevor wir gehen, muss ich die Rechnung noch bezahlen.

This means the same thing.

When the subordinate clause comes first, the main clause still follows the normal German rule that the conjugated verb comes early, in second position:

• Bevor wir gehen, muss ich ...

Notice that after the comma, German does not say ich muss first in the usual way if something already occupies the first position. The whole Bevor... clause counts as position 1, so the verb muss comes next.

Often yes, but there is a small difference in usage.

• bezahlen usually takes a direct object:
  • die Rechnung bezahlen
• zahlen is also common, but often appears with what is being paid for or with an amount:
  • Ich zahle die Rechnung.
  • Ich zahle für das Essen.

In everyday German, both die Rechnung bezahlen and die Rechnung zahlen can be heard, but bezahlen is very natural in this sentence.

Because in German, subordinate clauses are normally separated from the main clause with a comma.

So:

• Ich muss die Rechnung noch bezahlen, bevor wir gehen.

That comma is required in standard German.

This is different from English, where punctuation around subordinate clauses can be a little more flexible in some cases. In German, commas with subordinate clauses are much more systematic.

Not always. In many everyday situations, müssen is often better translated as have to rather than the stronger English must.

So this sentence often sounds most natural in English as:

• I still have to pay the bill before we leave.

Using must is not wrong, but in normal conversation have to often captures the tone better.

Because verbs are often translated according to context, not word-for-word.

The basic meaning of gehen is to go, but in a sentence like:

• bevor wir gehen

the most natural English translation is often:

• before we leave

That is because in English, when people are in a place and are about to go away, leave sounds more natural than go. German still uses gehen very naturally in that situation.