what is RAID and how does it work?

RAID = Redundant Array of Independant disks

The concept is rather simple. I would explain, but I'll just probably end up confusing you. I found a really good descriptiton at howstuffworks.com. Here's the link:

Link To Article

Well, RAID can provide a couple of uses. In short, it is where you store data on multiple harddrives that act like a single harddrive. This has 2 benefits: data recovery/backup, and faster speed.