Wir müssen zwei Löcher in die Wand bohren, bevor wir das Regal montieren können.

Because German modal verbs like müssen, können, wollen, and dürfen usually work with a second verb in the infinitive.

In a normal main clause:

• the conjugated modal verb goes in the second position
• the main verb infinitive goes to the end

So:

• Wir müssen zwei Löcher in die Wand bohren.

Literally, the structure is closer to:

• We must two holes into the wall drill.

That is normal German word order with modal verbs.

For the same reason: bohren depends on the modal verb müssen.

In German, when a modal verb is conjugated, the other verb stays in the infinitive and usually goes to the end of the clause.

So:

• Wir müssen ... bohren
• wir ... montieren können

This is one of the most common sentence patterns in German.

This is about the preposition in, which is a two-way preposition. That means it can take:

• accusative when there is direction or movement toward something
• dative when there is location and no movement

Here, bohren implies drilling into the wall, so German treats that as direction/change of location. Therefore it uses the accusative:

• in die Wand

Compare:

• Wir bohren ein Loch in die Wand. = into the wall
• Das Loch ist in der Wand. = in the wall / located in the wall

So die Wand is accusative here, not nominative.

Die can be nominative feminine, but it can also be accusative feminine.

For die Wand, the forms are:

• nominative: die Wand
• accusative: die Wand
• dative: der Wand
• genitive: der Wand

So in this sentence, die Wand is accusative, even though it looks the same as nominative.

Loch means hole. Its plural is Löcher.

So:

• singular: das Loch
• plural: die Löcher

After a number like zwei, German uses the plural noun:

• zwei Löcher = two holes

The plural changes the vowel (o → ö) and adds -er, which is a common German plural pattern.

Because Regal is a neuter noun:

• nominative: das Regal
• accusative: das Regal

In this sentence, montieren takes a direct object, so das Regal is in the accusative. But since neuter nominative and accusative look the same, the article stays das.

Because bevor introduces a subordinate clause.

In German subordinate clauses:

• the finite verb goes to the end

If there is also an infinitive with a modal verb, the infinitive comes before the conjugated modal at the end:

• bevor wir das Regal montieren können

This is the standard order.

Compare:

Main clause:

• Wir können das Regal montieren.

Subordinate clause:

• ..., bevor wir das Regal montieren können.

No, German normally needs the subject in the subordinate clause.

The sentence has two clauses:

1. Wir müssen zwei Löcher in die Wand bohren
2. bevor wir das Regal montieren können

Even though the subject is the same in both clauses, German still repeats wir. That is normal and required here.

Bevor means before and introduces an action that happens earlier than the action in the main clause.

Here the order of events is:

1. drill two holes in the wall
2. mount the shelf

So bevor connects those two actions and shows the time relationship.

It works like English before, but in German it creates a subordinate clause, which affects word order.

Yes, that is possible, but the meaning changes slightly.

• bevor wir das Regal montieren können = before we are able to mount the shelf
• bevor wir das Regal montieren = before we mount the shelf

With können, the sentence emphasizes that drilling the holes is a necessary step that makes mounting possible.

Without können, it is a little more neutral and simply states the sequence of actions.

All of those verbs are possible in some contexts, but they are not exactly the same.

• montieren = to assemble or install something, often by attaching it properly
• aufbauen = to set up or assemble, often furniture or something made of parts
• anbringen = to attach or put up on a wall or surface

For a shelf fixed to a wall, montieren is very natural because it suggests proper installation.

Depending on context, you might also hear:

• das Regal anbringen = attach the shelf to the wall
• das Regal aufbauen = assemble the shelf

But montieren fits very well in this sentence.

Yes. You can say:

• Bevor wir das Regal montieren können, müssen wir zwei Löcher in die Wand bohren.

That is completely correct.

Notice what happens in the main clause after the subordinate clause:

• the conjugated verb still comes second
• so you get müssen wir, not wir müssen

This is the normal verb-second rule in German.

Yes: bohren often appears with expressions like:

• ein Loch bohren = drill a hole
• in die Wand bohren = drill into the wall

In this sentence, German uses both ideas together:

• zwei Löcher
• in die Wand bohren

That is a very natural way to say drill two holes into the wall.