What's that supposed to mean? It sounds boring.

But it's not! What I mean by structure is that your story has to move along purposefully. It should start at an interesting point and lead to a resolution (a conclusion) that's satisfying to the reader. And it should have all of the elements of character (such as motivation—why Jon wants revenge against his stepfather) and background to make it feel believable to the reader.

Think of it this way:

How far would you get in a 100-yard dash if you didn't have a skeleton?

Answer: not far. Your muscles would be flopping around with nothing to pull against, and you'd be sprawled on the ground like a beached jellyfish.

That's a story without structure.