Wenn es regnet, nehme ich lieber die U‑Bahn als den Bus.

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Breakdown of Wenn es regnet, nehme ich lieber die U‑Bahn als den Bus.

• es: it
• regnen: to rain
• der Bus: the bus

Questions & Answers about Wenn es regnet, nehme ich lieber die U‑Bahn als den Bus.

Why is there a comma after Wenn es regnet?

Because Wenn es regnet is a subordinate clause (it starts with the subordinating conjunction wenn). In German, subordinate clauses are normally separated from the main clause with a comma:

• Wenn es regnet, …
• …, wenn es regnet.

This comma is essentially mandatory in standard written German.

Why is the verb nehme in second position even though the sentence starts with Wenn es regnet?

German main clauses follow the V2 rule (the finite verb is in position 2). When you put a subordinate clause first, that whole clause counts as position 1, so the main clause verb comes right after it:

• Wenn es regnet, (position 1) nehme (position 2) ich …

So you don’t say …, ich nehme… in this structure.

What exactly is wenn doing here—does it mean if or when?

Wenn can mean both when (recurring/general situations) and if (a condition). In this sentence it’s the common “whenever/when” sense: in the situation that it’s raining. Context decides, and German often uses wenn where English might choose either if or when.