A mole is just a number, like a billion or a trillion. So a billion in numeric form looks like 1,000,000,000 and a trillion is the same thing with 3 more zeros, or 1,000,000,000,000. If you looked at these numbers in scientific notation, they would be 1 x 10^9 and 1 x 10^12, where the exponent is actually the number of zeros in the number. A mole then, is actually the number 6.02 followed by 23 zeros, or 6.02 x 10^23, which is a huge number, and is used to count particles (atoms, ions, or molecules) since they're so small. To calculate values in chemistry, if you know the number of grams a substance weighs to make a mole of that substance, or grams per mole, and you have a sample of so many grams, you can find out how many moles that sample has, so
weight of a sample in grams / grams per mole = # moles, or
g(sample) / g/mole = moles, or as my chemistry teacher used to tell me, "grams divided by grams per mole equals moles!"
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