In bios set SATA configuration to RAID, then save and exit
it will reboot and on the screen after your POST you should have option to press Ctrl + I, this will then let you setup your RAID configuration
its not really relevant for RAID setups, its for old IDE set ups, if you have 2 optical drives and/or 2 HDD's the master is the first boot priority and the slave is the second, these are BIOS options nowadays anyway