Sound/midi question

Hello all Where to look for a _really_ basic explanation of how sound/midi (yes I know they're two distinctly different thingies) work with Linux? What I'm after is something that explains how they connect to the system, and how they're controlled... I want to set up some multitracking midi/audio SW (maybe Jazz is what I'm looking for) and as such I would like to *really* understand how everything fits together. Then, along the way, I might understand why my CD-rom seems to play through some audio-channel on the mixer instead of through the CD-input... (yes it's plugged in) Any suggestions? Jon