What causes the radiation we receive from cell phones, airplanes, microwaves,etc?

My mom might have cancer and I was doing some research, apparently cancer is not one disease it is multiple. Which makes sense because of how it happens with all the cells and what not. But I'm wondering with all the things that give us radiation and the fact that we use radiation as a treatment, is there a way to block the radiation from entering us? I know I might sound stupid but I'd just like to know what causes the radiation?Please get all scientific, because I want to know to the very last detail. Thank you