Pay what you want means you can pay whatever you want for something. It's like when you go to a store and you buy a toy, you need to pay its price because it's the amount of money it costs. But with pay what you want, you get to choose the amount of money you will pay for something, like a cool game, a delicious meal, or even a haircut.
When you pay what you want, you have to be responsible and think about the people who made that thing for you. They still need to earn money to support themselves and their families, so you should always try to pay what you think is fair. It's all about being kind and respectful to others while getting what you want at a price you can afford. Isn't that cool?