When you boot the server there should be a screen that says hit CTRL+Something to enter RAID config. you would enter that and configure the Disks for the array how you want them(RAID 1, RAID 5, etc..). Afterwards the OS would see each configured array as a single physical drive.
DISK 0 + Disk 1 as a RAID 1 = /dev/sda
Disk 2 + Disk 3 + Disk 4 as RAID 5 = /dev/sdb
The drive naming scheme may be slightly different (it can vary for some controllers) but the general idea is there.
( ^^ basically rehashing what inside man already said.)
Don't forget to check out Dells Linux storage page for more info on the PERC controllers in Linux and what management tools are available.