It is not explained well. The app leaves a permanent icon on your screen that exists no matter where you are or what other app you're in and I can't seem to use it as I think it is supposed to be used. This icon effectively has no purpose in my opinion. Therefore, control of how the robokiller app takes over control of your calls is also disconcerting. It didn't explain how I can interact with it to adjust. I was interested in this for the idea to annoy spammers but without control of who hears the annoying robokiller, then the call I want like friends, family and work will also hear the robokiller annoying recordings. I feel I am better off blocking calls on my own.