For Raid5 you'll need a minimum of 3 drives. Note Raid1 will not gain you any performance boosts, it's strictly for redundancy.
The setup of that raid will depend on whether your motherboard has a raid controller built in (hardware raid) or whether you have to do it through the OS (software raid).
If your motherboard supports it, you should create the array during the boot process. You'll have to enable the raid option in the BIOS (accessed by pressing DEL or F2 usually) then after that you should see a new option during boot that prompts you to press Ctrl+I or something similar to access the RAID setup menu.
If your motherboard doesn't have a built-in raid controller, you'll need to do it through the OS. If this is the case, post up what OS you're running.