It turns out it's more complicated than I thought, (oh, so you don't just jam wool in there and drag the other one through) so I found this useful video and now know at least a little more. I thought I'd share it since it's one of the best resources I've found so far.
These hand carders belonged to my great-grandmother, but, since we're pretty sure she didn't spin, we figure the original owner may have been her mother.
Luckily, (since I'm kinda wrecking the wool so it won't spin as nicely) a good part of the end product is going to my mom for felting and needle-felting, and I've heard it's been working well-enough for that so far. She dyed some with kool-aid, to make felt beads with, and I'm excited to check out the results in a few weeks when I see her next.