If you don't know what it is how would you know if you've been cheated out of it?
RAID has different levels depending on how many drives you have and what you need/want. As you have 2 drives you'll have either 0 or 1.
RAID 0 is where the 2 harddrives act and work as 1 drive to improve speed.
RAID 1 is where you have 2 harddrives and the second mirrors the other as a backup.
The partition(s) could be for the OS or to keep important files incase there is a problem, it all depends on how it's been set up.
RAID