How old is your child?
The age of the child matters. Per if they understand or not.
My kids have banks at home. They put their money in it. They decide if they want to spend it or save some for later.
They also have savings accounts.
We simply tell our kids, that if they spend all their money, they will have nothing left. So by trial and error, they have experienced this. First hand. If they want to buy something, we "help" them decide.... saying things like "is it worth it?", do you really need it or want it?, If you use your money now then how much will you have left? etc.
So then, it teaches them the PROCESS of the decision making.
Learning the PROCESS of how to use their money or not.
That is the key thing, that they learn.
My son is only 5 and he knows how to save his money or spend it.
My daughter is 9, and she knows how as well.
And they both understand the "cost" of things per the price tag. And if they want something in particular, they will save for it. Even my son, he can read and understand the price tags of things and what is "expensive" or not. And also they learn about math.