Basically, I drag the window over to the second monitor, and then hit F11. But instead of going fullscreen on that monitor, it goes fullscreen on my main monitor for some reason. I can't seem to find a way to drag it over or anything…
I'm new to having a two-monitor setup. Just got it running today. It's a bit of a strange setup, so if what I'm doing seems like it should be working, I guess I'll update the question with details on my setup.