Is there an idiots' guide to common 1st-year circuit elements? and what do I really need to know?

I'm currently in Circuit Theory I as part of my requirements, and my final project is to build two active passband filters that take input from an audio jack and put it out either to a woofer or a tweeter depending on the frequency. My TA, of course, is an Indian graduate student who knows the material but doesn't know how to explain it in a class with 20 students.

My two issues:

-The power amp we have to use is an LM386, and I've gotten it to work by blindly following a spec-sheet to connect it, but I don't know the theory like I do op-amps (LM741s, specifically) because those we've covered in class as a topic while we haven't covered this type of power amp. In addition, we've only treated these as black boxes and haven't gone into the spooky black magic that makes them work- is that a concern for a MechE?

-The actual audio jack. From looking at the diagrams on Wikipedia, I think the input source I'm using is going to be unbalanced stereo (running straight from an mp3 player/phone via a 3.5mm male-male cable), which I *think * means that the 'sleeve' should go to ground and the other two should act as sources- but since I'm using a mono speaker setup and only differentiating between signal frequency, should I just use both of those as inputs? and if so, how would I go about connecting such a circuit?

Tl;dr-

LM386: What?

3.5 mm stereo audio input: how?