[Voice]
Really, you haven't? [Never seen rain before? That's pretty incomprehensible...It storms even in the desert at times, after all.] Where did you live that it never even rained?
[Well, seeing as she works with the human body's electricity, she kind of had to learn some of the reasons for lightning in particular. So why not try and explain what she can?]
...It's a little complex from what I remember, but water evaporates into the air from sunlight, then these group together to form clouds. Then later the clouds will drop water, which causes rain. Then eventually water will evaporate again and keep the cycle going.
Lightning also comes from these clouds when they get thick enough. The water droplets form a static charge - that's the same sort of thing as what shocks your fingers if you touch a doorknob sometimes, but on a bigger scale. Eventually this discharges in a current down to the ground. I guess even dust and ash in the sky can cause lightning too, so it's not just water either.
And thunder's just the sound lightning makes...I guess they think it's because of hot air that the lightning makes. [She doesn't quite get that part though - it's more in the realm of alchemy, and isn't really as important as the electrical parts to her.]