What do we use to buy things we want or need?

Money is what we use to buy things we want or need, like handing over coins for an apple. Money works because everyone agrees it has value, so a shopkeeper will happily trade food or goods for it, trusting they can later use that same money to buy whatever they need.

Leaves and clouds have no agreed value and can't be exchanged for goods, so nobody would trade you an apple for a handful of leaves or a picture of a cloud.

Long before coins and paper money existed, people used barter, trading one useful thing directly for another, like a chicken for some bread, but that only worked if both people happened to want exactly what the other had, which is exactly the problem money was invented to solve.