RAID 0 is where the data is spread across 2 disks, and gives a read and write performance boost and storage efficient - disk space is combined 2+ disks.
Downside, if one disk fails all data is gone.
RAID 1 is disk mirroring, disk #2 is an exact copy of disk #1. No performance loss or boost max 2 drives.
Down side, only half disk space available (the equivalent of the smallest disk).
RAID 5 is striping with parity, like RAID 0 but the array uses space to hold the parity data used to rebuild a failed disk. Requires 3+ disks and boosts read/write performance. Can withstand a single disk failure.
Down side, one disk lost for parity purposes.
More can be read here if you so feel inclined:
http://en.wikipedia.org/wiki/RAID