What's the diff between photo stream and camera roll on iPhone 5

I was wondering why I was running out of room on my phone - then I realized I have double the pics taking double the storage on my phone! I was going through my camera roll and deleting a lot of junk pics and then I realized they were ALSO in the photo stream folder! How can I delete these pics JUST ONCE !?!?

Or just not have them in both places in the first place!

Message edited 12/12/2013 10:17:47 PM.