What does the new iPhone 5s do?

Today I went to the AT&T store and saw alot of people there
And I just wanna know what's difference between the new iPhone 5s and Old iPhones?

Itunes, Iphone 4s And Adding Music To It? - 1

Due to an Ios7 glitch when downloading it to my iphone 4s I had to complelety delete everything off my phone but I had my stuff backed up so everything is back on my iphone besides my music. My music is downloded not from itunes but from other websites.

I just click sync to put all my music back on my phone quickly but now I can't delete the music from my iphone on itunes and I can't drag and drop songs onto my iphone either. If I click manually select music it says its gonna delete all my music. What's a way to add all my songs quickly and be able to delete songs as well when I feel like it.

Buying refurbished iPhone off ebay?

My phone carrier is at&t and I want to buy an iphone off a third party site, such as ebay, and use it. Will i be charged by my phone company? What exactly would happen? My contract does not end for another year and i'm not willing to wait that long.

Updated to iOS 7, can't download anything?

So yesterday I updated my iPhone to iOS 7, but I had to delete all my music off my phone so there would be space to do it (its all still on my iTunes on my computer). Today, I plugged in my phone to re-download my music to my phone, but it's saying I don't have enough room because there's a huge thing on my phone called "documents and data" that was never there before and is taking up all of my space making my phone useless. What am I supposed to do to get rid of it? I've deleted everything and it isn't helping.

Added (1). I backed it up and nothing is left on my phone except my contact list and when I tried to find information on the Apple Customer Service page, it said my "coverage plan" (whatever that is) doesn't support me calling, and I would have to pay 70 dollars.