Wenn der Stau endet, können wir weiterfahren.

Because wenn introduces a subordinate clause. In German, the conjugated verb usually goes to the end of a subordinate clause.

• Wenn der Stau endet = when the traffic jam ends
• Structure: wenn + subject + ... + verb

Compare:

• Der Stau endet. = The traffic jam ends.
• Wenn der Stau endet, ... = When the traffic jam ends, ...

This verb-at-the-end pattern is very common after words like wenn, weil, dass, obwohl.

Because the sentence starts with the subordinate clause:

• Wenn der Stau endet, ...

That whole clause takes up the first position in the sentence. In a German main clause, the conjugated verb must come second, so the next part begins:

• können wir weiterfahren

So the structure is:

1. Wenn der Stau endet
2. können
3. wir
4. weiterfahren

This is called verb-second word order in the main clause.

Compare:

• Wir können weiterfahren, wenn der Stau endet.
• Wenn der Stau endet, können wir weiterfahren.

Both are correct.

Here, wenn means when or if, depending on context.

In this sentence, it is best understood as when:

• Wenn der Stau endet, können wir weiterfahren.
• When the traffic jam ends, we can continue driving.

A useful rule:

• wenn = when for repeated situations, general situations, or future situations
• als = when for a single event in the past
• wann = when? in a question or indirect question

Examples:

• Wenn ich Zeit habe, komme ich. = When/If I have time, I’ll come.
• Als ich klein war, ... = When I was little, ...
• Wann kommst du? = When are you coming?

Der Stau is masculine nominative singular.

• Dictionary form: der Stau = the traffic jam
• In this sentence, der Stau is the subject of endet, so it is in the nominative case.

That is why it is der, not den or dem.

Quick overview:

• der Stau = nominative
• den Stau = accusative
• dem Stau = dative

Here:

• der Stau endet = the traffic jam ends

Stau usually means a traffic jam or backup of traffic.

In everyday German, it is very common when talking about roads, highways, delays, and driving.

Examples:

• Es gibt einen Stau. = There is a traffic jam.
• Wir stehen im Stau. = We are stuck in traffic.
• Der Stau endet. = The traffic jam ends.

So in this sentence, it refers to the traffic congestion clearing up.

Yes, weiterfahren is a separable verb.

It means to continue driving or to drive on.

In a sentence with a modal verb like können, the full infinitive stays together at the end:

• Wir können weiterfahren.

But without a modal, it separates:

• Wir fahren weiter. = We continue driving.
• Fahrt bitte weiter! = Please continue driving!

So:

• with modal: weiterfahren
• without modal in a normal present-tense clause: fährt ... weiter

Because German normally uses a comma to separate a subordinate clause from a main clause.

So in:

• Wenn der Stau endet, können wir weiterfahren.

the comma marks the end of the wenn-clause.

This is required in standard German writing.

You will see the same thing with many other subordinating conjunctions:

• Weil es regnet, bleiben wir zu Hause.
• Obwohl er müde ist, arbeitet er weiter.

German often uses the present tense to talk about the future, especially when the future meaning is clear from context.

So:

• Wenn der Stau endet, können wir weiterfahren.

literally looks like:

• When the traffic jam ends, we can continue driving.

Even though the event is in the future, German does not need a special future tense here.

This is very normal. Compare:

• Morgen fahre ich nach Berlin. = Tomorrow I’m going to Berlin.
• Wenn er kommt, reden wir mit ihm. = When he comes, we’ll talk to him.

Because können is a modal verb.

Modal verbs combine with another verb in the infinitive:

• können = can / to be able to
• weiterfahren = to continue driving

So:

• Wir können weiterfahren. = We can continue driving.

In German main clauses, the modal verb is conjugated, and the other verb goes to the end in the infinitive.

That is why you get:

• können wir weiterfahren

and not something like wir können weiterfährt.

Yes, absolutely. That version is also correct.

• Wenn der Stau endet, können wir weiterfahren.
• Wir können weiterfahren, wenn der Stau endet.

The meaning is basically the same. The difference is mostly focus:

• Starting with Wenn der Stau endet puts more emphasis on the condition/time point.
• Starting with Wir können weiterfahren puts the main statement first.

In both versions, the wenn-clause still sends its verb to the end.

They are similar, but not always exactly the same.

• Der Stau endet = The traffic jam ends.
• Der Stau hört auf = The traffic jam stops / comes to an end.

In this context, both can work, but endet sounds a bit more neutral and straightforward.

You might also hear:

• Wenn der Stau vorbei ist, können wir weiterfahren. = When the traffic jam is over, we can continue driving.

That is another very natural way to express the same idea.

Yes. Wenn can mean both if and when.

You decide from the context.

In this sentence, when is the natural translation because the speaker is referring to a time point: the traffic jam ending.

• Wenn der Stau endet, können wir weiterfahren.
  = When the traffic jam ends, we can continue driving.

But in some contexts, if also works in English:

• Wenn es regnet, bleiben wir zu Hause. = If it rains, we stay home.

So wenn often covers both ideas: a condition and a time/event. English usually forces you to choose one, but German often uses wenn for both.