[Luke opens his mouth before realizing he's not really sure how to explain it. If she's never heard of a lightsaber, she's never heard of a Jedi, right?]

[Best start at the beginning.] A lightsaber is the weapon of a Jedi. It works perfectly with their fighting style, and only Jedi can wield one safely. [He scratches the back of his head.] And I'm in training to become a Jedi.