DFU mode

two days ago i just realized my iPhone 6 went into recovery mode and after doing some research i realized it could be fixed using iTunes and when i attempted it was solved but i then logged in to apple store downloaded whats app and installed . Trying to setup the phone went back to recovery mode and when i tried fixing it again it went in to DFU mode. i have been trying to remove it from the mode but it wont go. it seems stocked. the normal white screen that comes up when the phone starts has changed to black.

please what can i do