So what's the deal with Re-Writable CDs?

Well, I sent my dad out to get me some blanks, and that's what he returned with. Don't get me wrong, I know /what/ they are [ and I kind of feel like a noob asking about them D: ] but tell me. So, is it like a normal CD? Use Media Player to burn music onto it and then be able to just pop it back in later to add more or take them off? Or am I totally on the wrong track here D: