Ask Electronics

I'll start off with your questions are a outside of what I know well. In general to do stuff with electronics, you don't need to know the physics behind it, but the equations that pop out. Mainly V=IR, Almost everything goes back to that. Behind the scenes are lots and lots and lots of differential equations. Alpha Pheonix has a few good visualizations for resistance. He has a water based demo to visualize voltage and resistance, and a maze demo showing how electricity "finds" the path of least resistance. ElectroBoom probably won't teach you too much, but can show some interesting things you can do. EEVblog has some good lectures. For specific applications Digikey and Texas Instruments have some basics, and there are many lectures online available.

I think the questions you asked are a little more on the physics side than the electrical side, and the specifics I think of as a dark art that comes with experience. In general most capacitors you see are blocking DC on an AC circuit, coupling capacitors that are smoothing the power circuit, or capacitors to control/tune something specific. Those control values would be given in a datasheet. Resistors are often going to be current limiting, voltage dividing, or "pulling" a high impedance signal. To design something you often just need the rule of thumb, and not necessarily a deep understanding of "why".