What is the mole used to count?
The number of atoms or molecules in a given mass of stuff.
It is a fact that
The mole is thus the link between the micro world of atoms and molecules, of which we can conceive but not observe, with the macro world of grams and kilograms, that which we measure on a laboratory bench. If we can measure the mass of a pure substance (or measure the volume expressed by a gas) we have an excellent estimate of the number of atomic particles the substance contains.