The mole represents a scale-up from atomic mass units to grams. Instead of counting molecules, an impossible task, we can count moles. How many molecules are there in one mole of a substance? We really do not need to know this to use moles in solving chemical problems, any more than the hardware store clerk needed to know how many bolts there were in a pound. But there are situations when this knowledge is useful.

The number of molecules of a substance per mole is called Avogadro's number and given the symbol N.
(By the way in which a mole was defined as an amount of a substance in grams, equal in numerical value to its molecular weight in amu, Avogadro's number also is the number of amu per gram.)