Explain the "No Fly List"

President Obama made a big deal about the "No Fly List" during his speech.
Why should someone on that list be allowed to buy a gun?
Before having to ask that question, a few good questions.

• How do you get on the "No Fly List?"
• If you are put on the list by mistake, how do you get off it?
• How many people currently on the list have bought guns?
• How many of those have committed crimes with guns they bought?

Just saying "No Fly List" sounds good.
But there are more questions than answers right now.