What is the mole and how to calculate number of moles?

The Mole 
One mole of an element is the amount that contains the same number of atoms as there in 12g of carbon 12
This number of atoms that are found in one mole is the Avogadro’s constant = 6.0X 1023mol-1
Molar mass: is the mass in one mole of an element.
Relative atomic mass for C= 12g
Molar mass of carbon = 12g/mol
Amount in moles = mass/molar mass
  n= m/M mol

Example:
What is the amount in moles of carbon in 30g of carbon?
Answer:
given quantity X conversion factor = desired quantity
given unit X (desired unit/given unit) =  desired unit
grams of carbon → moles of carbon
12 g of carbon → 1 mole
Grams of carbon = 30g X (1mol C/ 12g C) = 2.5mol