I didn't really understand voltage drops across resistors, so I researched that. I looked up various tutorials, but they all focused on how to calculate voltage drop, which didn't really help me understand what it is. Eventually I resorted to Wikipedia, which helped a bit.
I had been thinking of voltage drop as something that happened locally across a single resistor, due to the resistance partially blocking the "pressure" of the voltage. Thinking of it as the energy lost makes more sense to me as to why you have to consider the circuit as a whole in order to calculate it. Related to that, I verified experimentally something that I had read in the tutorials but didn't quite get: that it doesn't matter which side of an LED the resistor is on.
I'm still not sure I fully get why resistance and voltage drops work this way, but I'll return to it later.
I didn't have the components to really do the switch lab, because Adafruit messed up my order and shipped me a kit with no switches. So I just plugged and unplugged wires on my breadboard in order to play around with serial vs parallel switch arrangements.