Recently I was out shopping for a pair of binoculars...... and I had no idea what the 2 sets of numbers mean (8x42, etc.) Found Dr. Binoculars lesson - they are short and tell you the basics quickly. http://www.binoculars.org/drbinoculars/lessons.html In case you want to know quickly: the first number is the magnification power and the second number is the size of the objective lens.
So in 8x42: 8: Is the magnification power - which means while looking at objects through the binoculars, everything will look 8 times as close as when looking with the naked eye. 42: Is the size of the lens in the front of the binoculars. The bigger these are more light enters the instrument and makes for a brighter scene, but also makes for bigger binoculars. Also: an 8x20 and a 8x42 binocular both have the same magnification. Only one is bigger (the one with 42) and makes for a brighter scene.