How to use Odin?
BL = Bootloader. Select Bootloader for firmware. Only used if BL file is available. Separately flash bootloader by selecting this option.
AP = PDA in older versions of Odin. Mostly used to flash firmware. If there is one tar.md5 file, then AP will be used to flash.
CP = Phone in older versions of Odin. When modem related stuff are updated, then this file will be provided.
CSC = Consumer Software Customization. This is used for carrier related stuff. Also CSC contains region information such as country code and APN settings.
Mass D/L = Multi device download. You can download one firmware on multiple devices. Must be exact same model (ie. SM-G950U).