What is a mole?

A mole is like a dozen - it is a number of something. You can have a dozen people (12 people), a dozen oranges and so on. A dozen is useful for big objects like oranges, but atoms and molecules are much much smaller. While a dozen means a count of 12, one mole is a huge number, 6.022x10^23 to be exact.

But since atoms and molecules are so tiny, one mole (6.022x10^23) of water molecules will be weight roughly 18 grams. A mole of carbon atoms 12 grams, a mole of gold almost 200 grams, because an atom of gold is much larger than a carbon atom. Even though the masses of a mole of water/carbon/gold are different, the number of atoms/molecules in each of them remains the same! 

[here it would be very helpful to show a classical photo of moles of different elements/molecules in conical flasks]