BL = Bootloader. Used for firmware bootloader. AP = Flash firmware image. CP = Modem update. CSC = Country/carrier settings. Mass D/L = Flash to multiple devices of same model.

Auto Reboot: Reboots phone after flashing (Recommended: ON)
Re-Partition: Use only with PIT files (Recommended: OFF)
F. Reset Time: Resets counter after flash (Recommended: ON)
Nand Erase All: Erases all data (Dangerous!)
Flash Lock, T Flash, Phone EFS Clear: Advanced options, use with caution.