Before you think about installing RAID, consider carefully if it's really what you want and what it will do to improve your computer and computing experience.
Very often, people have very high hopes of RAID and think it is the cure for all ills. Well, it isn't. It can be very difficult to set up, especially in an existing system and when it is set up, it does not achieve what a lot of people think it will, nor is it supposed to.
RAID has very limited use in a normal home/small office environment and you disk capacity would be better utilised in the conventional way.
A better use for your second hard drive would be as a conventional full system backup.