What is meant by mole concept?

$6.02\times {10}^{23}$ entities together constitute a mole. This number is nothing but actually the ration of a gram to atomic weight unit. In this way, one mole of a substance will have the same magnitude of mass in grams that a molecule/atom/ion of that substance has in amu.
This number $6.02\times {10}^{23}$ is known as Avagadro's number.
If we have a given weight of a substance, then the number of moles is given by:
$\frac{Givenweight}{Grammolecularweight}$
Also, the volume occupied by one mole of an ideal gas at STP is 22.4 litres.