Have you ever wanted something really badly, like a new toy or candy, and you were willing to give your own money to get it? That's kind of like what willingness to pay means.
Willingness to pay is when you decide how much you are willing to pay for something you want. It's like making a deal with yourself - you decide how much the thing you want is worth to you and how much you are willing to spend to get it.
For example, if you really, really want a toy that costs $10, you might decide that it's worth spending all of your saved-up allowance money to get it. That means your willingness to pay for the toy is $10.
Businesses and stores also use willingness to pay to help decide how much to charge for things they sell. They try to figure out how much people are willing to pay for something so that they can make a profit.
So, willingness to pay is all about deciding how much something is worth to you and how much you are willing to spend to get it.