If all you need is more capacity, you would be better off to simply add a additional HD. For home users, the choice is normally between RAID 0 and RAID 1. With RAID 0 you get double speed reads and writes. However, if one disk fails, you loose EVERYTHING stored on the computer. With RAID 1, you have a mirrored array whereby all data is stored (mirrored) on the second drive. It gives double speed reads, normal speed writes. If one drive fails, everything is still available on the second drive and the machine is still bootable. Also note that with RAID, all drives must be identical, or minimumly, the same capacity. Using drives of different capacity will result in the RAID using the smaller drives capacity as the base capacity. Excess capacity on the larger drive cannot be used, not even to create an extra partition. If need pure speed, RAID 0; if you need data security, RAID 1; if you simply need capacity, add a HD.
