RAID 0(Striping) takes two drives of the same size and creates a bridge between them to make them act as one large drive. For example two 250GB drives would show up on the system as one large 500GB drive. This increases the speed of data being processed as it writes and reads across both drives. The downside is there is no data security. If one drive goes down in the RAID 0 configuration all data is lost as half is stored on one drive and the other half on the other. This is best used for situations where the data is not critical, but a speed performance increase may be desirable such as when using the machine for gaming.
RAID 1(Mirroring) takes both drives and uses one to create a real time backup to the second. In this case two 250GB drives will show up as one 250GB drive. This is a good setup for those looking for data security as information put on the main drive of the RAID will immediately be copied over to the other drive as an exact match. You do lose some speed due to the extra processing, but allows for the data to be saved if one of the drives in the RAID go down. Simply replacing the defective drive will automatically rebuild the array over a short time.