Když je vítr studený, beru si kabát.

When the wind is cold, I put on a coat.

Breakdown of Když je vítr studený, beru si kabát.

• já: I
• být: to be
• studený: cold
• když: when

Questions & Answers about Když je vítr studený, beru si kabát.

Why is když used here? Could I also use až or jestli?

Když means “when / whenever” in the sense of every time that and is used for general, repeated situations or facts.

• Když je vítr studený, beru si kabát.
  = When(ever) the wind is cold, I (habitually) take/put on my coat.

Až is more like “when (once)” for a single, usually future event:

• Až bude vítr studený, vezmu si kabát.
  = When the wind is cold (at that future time), I’ll put on my coat (once).

Jestli is mainly “if” (a condition, not a time that you’re sure will come):

• Jestli bude vítr studený, vezmu si kabát.
  = If the wind is cold, I’ll put on my coat.

So in your sentence we talk about a general habit, so když is the natural choice.

Why is the word order je vítr studený and not vítr je studený?