Describe intention directly before ask a question

Before asking a question, It's a good habit to describe your intention clearly. Below is a real story happened between me and a coworker.

CW: Hey, do you know how to do B on windows?
Me: O, yes. You can:
1. Blah
2. Blah
3. Blah
But why you want to do this?
CW: Hmmm, because I want to do.
Me: Do? Why ask B? They're not related.
CW: Why? According to concept C, A is controlled by B.
Me: No, you misunderstood concept C. It's blah
CW: O, I see.

If he asked how to do a at the beginning, we both can save a lot of time.
When we need to ask a question, it's a sign that we don't understand the stuff very well. then we 'd better describe our intention directly. if we ask a different topic by our own deduction, which may be a misunderstanding, we may be on the wrong track.