To clarify, you're confused by the fact that carbs are broken down, only to be built up again into glycogen, and sugar is converted to something even more simple, only to be built up and stored again?
If that's what you're not understanding, then I can def. understand.. Assuming that's what it is, I hope this helps:
Carbohydrates/Starches are plants' main method of sugar storage (similar to our own glycogen storage), so before we can lodge sugar into our own muscle from carbs, it must be built into something that our body can work with, in this case, that is glycogen.