Ill touch at the topic abit, although I must admit I don't know everything.
So RAM is I guess the memory you have on your computer, and I beileive it affects how fast things are.
Hard Drive is the amount of space on your C drive that it can hold. Ex. Most programs take up some space on your HardDrive/C drive.
Graphic Cards are chips that enhance the graphics on your computer. Mostly used for better game play.
Well Kiros can explain everything else from here