There are several RAIDS, but the main ones are RAID0 RAID1 and RAID5
RAID0 is combining 2 drives to make it appear you have 1 drive having the space of the two drives. This gives you a speed increase.
RAID1 is having a mirror of the other drive, so if one fails you still have the information. Great for a server.
RAID5 is having a minimum of 3 drives with one of them being used as a backup per 5 drives, so you can get all your information back if any one fails. But it has a sacrifise of speed.
Cisco CCNA, Comptia A+, 1/3 through CCNP