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Hey, I'm an amateur photographer and I was just wondering if anyone more experienced than I am can tell me what these things mean.

Shutter Speed: 1/251 second
Aperture: F/2.8
Focal Length: 6 mm
ISO Speed: 80
Sensor Size: 4mm

I've taken these numbers from what my camera does.

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I'm pretty n00b but I will explain what I can.
And of course if you need more clarification there are tons of tutorials on DA and google comes in handy.

The shutter speed is how fast or slow your shutter goes. . . slower shutter speed will take in more light but anything that moves at all will be blurred, faster will take in less light but may or may not be effected by motion.

The aperture is basically how much light it brings in. . . the larger the number the less light, the smaller more light. basically it functions like your pupil.

Taken from http://www.photoaxe.com/understanding-the-lens-focal-length-and-aperture/ :
"The focal length of a lens determines its angle of view, and also how much the subject will be magnified for a given photographic position.
Focal length also determines the perspective of an image.
Longer focal lengths require shorter exposure times to minimize burring caused by the shake of hands."

here is something on ISO http://www.slrphotographyguide.com/camera/settings/iso.shtml

something on sensor size: http://www.digicamhelp.com/camera-features/camera-parts/sensor-size/