Um... In general...
-Scratches the side of his head-
I'm not too sure, really. Keyblades are light, used to fend off darkness. What the Organization wants you to do is defeat certain kinds of darkness called "Heartless." They're the darkness in our uh... hearts. A magic kind not the actual beating one. And when the Keyblade is used to defeat them, they release a heart back to light.
Uh... That might've sounded a bit complicated, but that's what they're for.
At the end of the day, though, for you, it's just a big magic key you can do whatever with.
-Grins-
mario is red, i am green, i try my best, but everyone's mean[and as the bird flies away...]
Unlimited Blade Works!
[A whoosh of fire is heard as the thuds stop. The sounds of the bird entering a black hole are eventually heard, and miscellaneous noise as Archer didn't stop the recording.]
…
...If I give myself up, will you stop?
make it through this year if it kills you yet | 2001-2019Light, and darkness...
Those are terms I'm kinda familiar with from back home... heros are light, and bad guys are darkness... I think they're also magic elements.
But, I like the last explanation you gave!
-she smiles-
So uh... will you and the other keyblade wielders show me how to use it?
All our wishes can come true

hmmm.... maybe...
all this keyblade and kingdom hearts stuff seems kinda complicated...
...
But I'm willing to learn!
-she grins again-
Ok... um...
I guess, and this is pretty general but.... what am I supposed to do with it?
I saw Roxas fighting with it, I can unlock things with it, and the guy in the coat wanted me to... collect hearts with it?
...
And... what does he mean by, collecting hearts?
All our wishes can come true