1) Your processor is the heart of the computer. It does the computations. All those 1's and 0's in your computer get mashed there. The number of cores (in really basic terms) is how many 1's and 0's it can smash simultaneously, and the speed (Ghz) is how quickly it can smash them. The general rule is, if you are doing a lot of different things (music, video, game, internet browsing, etc) all at once, you want more cores. If you are doing one or two very intensive applications (modern gaming) you want a faster core speed.
2)RAM is where it stores information when it's using it, but can't currently put it in the processor. The more of it, the better. It will greatly increase your computer's ability to multitask without having to access the hard drive (which, in computer terms, takes a long time). The standard you want to have now-adays is about 1-2Gb with high end machines being closer to 4 or 8.
3) RAID Cards allow you to use multiple hard drives more effectively. Some of them allow for hard drives to back up onto each other, others allow you to use multiple hard drives as single, large logical partitions. Great article http://en.wikipedia.org/wiki/RAID for more information.
4) SATA and SCSI are two different types of ways to connect your Hard Drives with the rest of the computer. SATA is much cheaper, SCSI is much faster. Pretty much the only time you will see SCSI is in file server computers where there is a large need to access the hard drive quickly.
5) I'm not sure on this one actually. A PCI Express card is a standard card you plug into your computer's motherboard to give it some kind of additional function (usually video cards, memory card readers, or extra ports) but the Fibre Channel thing, I've never herd of.
Hope that helps, sorry for the wall of text.