Why can I not see my iPhone's music listed in iTunes the way my computer's music library is listed?

Cannot see device music libraries in iTunes, which makes it virtually impossible to add or delete music when devices (4s, 5c) are connected to computer. Wanted to use my 4s as an iPod, but cannot see the library in iTunes in order to add, delete, or just see what music I have on my devices. Can't load purchased ringtones to my 5c, get the message that everything on the device will be erased. Also get that message when I try to add new music to my 4s, plus now my Nano demands to be reset every time I try to sync, which will erase everything on my iPod. What am I doing wrong? These newer versions of iTunes are terrible, I cannot manage my devices like I could in the past. Would greatly appreciate any help!