"Why learners" want to know why they should care - why should they be learning this, why it is important and why they need to focus on it.

"What learners" want the facts and want to know what you're going to be explaining to them. Give them an outline or step by step process. The bottom line for them is - "What do I need to know?

"How does it work" learners need to see the relationship between what they are learning and the big picture. How does what you're teaching them actually work.

"What if" learners will want to know that you've considered the alternatives. They'll want to know why it is done the way you outline and whether another way is better. They need to understand the boundaries and issues that were considered in marking the decision to do it this way.

This article itself follows the 4Mat system - so it can help you to structure your content as well.