I added some papers related to SHs just now, but I would strongly recommend you to check the section about SHs in "Real-Time Rendering" (always check this one if you come up with questions about fundamental real-time cg stuff) and "Physically Based Rendering" (if you got this one too in the meantime). Badly I need to get productive regarding our Uni software project so I've not time to give you a personal explanation atm.