Safe to delete the pictures from the camera roll, without them being deleted from iCloud drive? 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&amp;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..
iCloud Drive is just a way to sync photos and other files between all your iOS devices and computers (both Mac and PC). iCloud does not function as a standalone Cloud storage service, hence if you delete photos from your iPhone they will also be deleted from iCloud Drive. 

You can however upload your photos to other Cloud services like Dropbox, or simply transfer the photos to your computer (i.e. into another folder or import them into photo management software such as the Photos app on macOS), and then delete them from your phone and these photos will still remain on your computer or Dropbox.