when I scan for issues and it find some problems before it fixes them it asks if I want to back-up the registry. I don't know I i am supposed to or not
Its asking you if you want to back up what its about to clean. To be honest I don't back up anything when I use ccleaner but if your hesitant you might want to allow it to create back ups and keep them for a couple of days just to make sure everything is ok. I will tell you that I have never seen a problem come out of using ccleaners issues scan though.