When dealing with large quantities of something, it is often convenient to define a term that refers to a certain quantity. For example, a dozen of anything is 12. If I buy 3 dozen doughnuts, I have purchased 3*12=36 doughnuts.
In dealing with large quantities of molecules, the term mole refers to 6.022×1023 molecules. This number is referred to as Avogadro's Number.
1) Suppose you have 3.02 moles of a certain type of molecule. How many molecules do you have?
Using the idea of a dozen as an example again, if you have 2 dozen blocks and their total mass is 48 kg, the mass of one block would be 2.0 kg.
2) Suppose you have a sample of 3.46 moles of a certain type of molecule and the total mass is 87.9 g. What is the mass of a single molecule?