"What I want to ask is the following" sounds better in this context because it follows the statement right after. "Below" is when it is listed further down the page. Below you will find the following key concepts: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

You can use "the following" when writing, or when speaking. ("The following are the reasons why you should study every day...", "The following is a story about something that happened to me last year.") Using "below" in this context, you are literally directing someone's eyes to the writing below the thing they are reading, and also, it might not be directly below (I mean there could be a paragraph or two in between). So it's best not to use in speech. Similarly with "above" it's referring to something that was written higher up on the page but not necessarily directly above. (And I'll note here that the opposite of "the following" is "the preceding".) Also note that when used as an adjective, the placement of these words will differ: "The discussion below will address the problems facing the world." "The following discussion will address the problems facing the world."