A mole is a name given to a certain number of particles. Amounts of various substances are measured in a unit known as the mole (known as mol for short, symbol n).
One mole is approximate 6.02 x 1023 particles (this number is known as the Avogadro constant, NA)
Number of moles = Number of particles you have ÷ Number of particles in a mole
For example: I have 1.5 x 1024 C atoms - how many moles of carbon do I have?
Number of moles = (1.5 x 1024) ÷ (6.02 x 1023)
= 2.49 moles