For flashing anything custom (or even stock) on your phone it's required to flash it in download mode. To enter this it's most of the time the same combination (while phone is off): power on button + home button + volume down. On the S8 it's bixby instead of home.
You can download most recent odin program Please login to see this link.. The AP tab is used to flash full roms, kernels or recoveries. BL is meant for bootloaders, CP for modems and CSC obviously for CSC files ^^
- Out of my head :)