What does each of these computer terms mean: memory, hard drive, and processor?

Im looking to buy my first laptop, and I am confused as to what each term means in the computer world. can anyone provide me with insight, so I can understand? thanks in advance.
Update: I also want to know does it matter what brand of laptop i purchase, such as Dell, HP, or Gateway?? Or can I just purchase any brand with sufficent amounts of memory and a nice hard drive size?
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