Yes, for our purposes scratch the polarity and think AC source fro signal.
The example schematic shows the simplest example, with a series R and a shunt R. In real life a signal encounters R, C and L. L is usually left out because its so small. But in a power supply or wah-wah pedal, it becomes important.
Really we mostly deal with R and C. Those two values, Zs and Zl, stand for impedance in series with the signal and impedance loading the signal. That impedance can come from a resistance, capacitance or inductance. Or (in real life) all together. But we measure impedance in ohms, like R, but it changes with frequency.
The way a cap works we can think like this: at some high frequency it has no impedance to the signal. At some low frequency the cap treats it like DC. You can make that reactance into an ohm value. With a simple tone control type filter we are putting a C in one direction and an R in the other. At the frequency where the signal sees equal "resistance" (really impedance) in both directions you have 1/2 the voltage, 6db less signal.
