MuscleWiki: Find exercises that work specific muscles
As someone who knows almost nothing about muscle building, why would I want to work specific muscles?  How do I know which muscle I should want to work?  Do I look at a particular muscle and feel it's too small and that's how I choose?  Do I target specific muscles that feel sore after I do some other activity that is the real activity I value?  I'm genuinely curious.  If this website is giving the "how", I want to know the "why".