Q: How do I get all my iPad pictures back onto my computer after I've deleted them from my computer

I have pictures on my iPad, they are all in my camera roll, my photo stream seems to have less pictures and contains some pictures that I have removed from my camera roll still. I uploaded the photo stream to my PC and then noticed that they were mostly the ones I had previously deleted from my camera roll but must still have been in my photo stream so I deleted the whole album on my PC, everything is still on my iPad. What I'd like to know is #1 why is my camera roll and my photo stream different, and how can I ask my icloud to [re]- upload all the camera roll or photo stream pictures back to my PC again, because they are all still on my ipad.