Do you need a refresher of what RAID is and the different RAID levels?
Maybe you need to easily explain what RAID is to a co-worker or boss.

LSI has a good nice page dedicated to RAID basics which:
1. Gives a brief description of what RAID is
2. Why you might want to use RAID
3. Super animated shockwaves to show how RAID works

I really like this high-level set of animated presentations, it has helped me explain RAID quite a few times.
Bookmark them for future use.
Just go to LSI - Redundant Array of Independent Disks to view for yourself.