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.)