What's the difference between "Asking a Question" & Start a Discussion"?

Not much. If you ask a question, you can declare one of the answers to be the best one and award a red ribbon.

wow I never knew that? I have seen the damn ribbons, but never knew I could select one. Can I go back and then select one for each of my questions?

I usually do not even notice which one I select - meaning discussion or question - whatever opens up I type in so I probably use it all wrong any way.

Yes, you can even delete one and give it to someone else - as long as it was a "Question".

Let me add something. Unlike a thumb, a ribbon goes into your profile as a "Question Answered".