Firstly, let me just say that I do know that similar questions might have been asked, but none seem to answer exactly what I'm wondering, and I cannot afford to guess in this case, as that may result in all my pictures disappearing. Notice that I am wondering about iCloud drive.
I recently noticed that I can go into the camera roll and one by one add the pictures I want to iCloud drive. What I don't understand though, is if they, after this, are saved there in a way that makes it completely safe for me to delete them from my camera roll (on my iPhone 6), without also losing them from iCloud drive. From what I have found online (online forums etc), this is not possible for "regular" iCloud, however I think all the threads I found were a bit old. An example of a thread I found: https://discussions.apple.com/thread/7604440?start=0&tstart=0 I could not find any answers concerning iCloud drive.
Note that I do not allow for my pictures to be automatically uploaded to iCloud/iCloud drive; they are only saved in my camera roll. If iCloud drive can work as its own storage, then I will choose which pictures I want to go there, and then delete them from my phone to free up some much needed space.
Hope someone can help me, I would be very thankful!! And when you answer, I would really appreciate it if you explained all the words, as I have very little knowledge about this stuff. For example, I have no idea what photo stream means (it came up once when I was searching this topic), so if that actually is a factor in this context, please explain it. I don't really understand the "help" pages on apple's homepage..