Derk Cavin writes "The demo of Kingdom Hearts 358/2 Days puts the player in control of Roxas and was divided into two playable missions that took place in Twilight Town and Agrabah respectively. Each mission comes with its own brief cutscenes, objectives, and rewards.
It doesn't seem like it's going to be possible to learn or equip skills mid-mission in the final version based on the game's text, so a lot of preparation needs to be done beforehand based on the mission description and tips. Players were unable to learn or equip skills between missions in the demo either, so we went in to a lot of these missions without anything more than what seemed like the starter keyblade. Defensive techniques such as blocking and dodge roll that were learned early on in the other Kingdom Hearts titles were probably absent from the demo as well, though it's possible that we simply couldn't figure it out due to some re-mapped controls."