This is not very good English. It would be better if it said, "When the sun shines (or is shining), I wear a shirt."
That's exactly what it says.
Must've been changed!
so what if it's rainy?
כשזה קורה, אני הולך בלי חלוצה
It's חולצה, not חלוצה.
would it be wrong to say מתי השמש instead of כשהשמש?
You could say "מתי שהשמש", though some say it's grammatically incorrect, and to me at least it doesn't sound great. I prefer כשהשמש, which also has the benefit of being shorter.
is used for questions ...
When the sun shines I put on a shirt.
I was marked wrong for that too. It should be accepted.
I hope so.
Is putting o a shirt related to avoid sun burn because of the shining of the sun? Or is the "shining" harmless?