[His ball of light metaphor wasn't stupid, gosh Katsa! Still, he looks very pleased with himself that she's managed that much, not even aware she may be second-guessing.]

Magic seems to be that way. [He holds up a hand, allowing himself to concentrate as well before the glow of fine lines appears in his palm.] You use this. Once you have a good handle on this, you start to think about creating the flames themselves. [It's a shaky transition at best, but the white light fades and turns into an unshaped, free-moving pile of flames in his palm.]

Everything about this kind of magic is physical manifestation. I don't know about the magic here with the shards, but this is a start.