newbie questions: about raid

[McCoy]

Hi,

I have some question about raid:

1. what is raid?
2. why we use raid?
3. what 's mean raid 0, raid 0/1, raid 1, raid 4 and raid 5?

I 'm new to raid and I have downloaded some howto and raid tools. But I
still have some confuse that whether raid is only the method to make
many disks an array or have other benefit?