Burden of proof is like playing a game where you have to prove something is true. Let's say you tell your friend that you can run faster than anyone else in the playground. Your friend might ask you to prove it by having a race. In that case, the burden of proof is on you, because you said something and you have to show it's true.
In philosophy, burden of proof means that if you are making a claim or saying something is true, then you have to provide evidence to prove it. So, if you say something like "the moon is made of cheese," someone might ask you to prove it. And if you can't provide any evidence, then you have not met your burden of proof, which means that people don't have to believe you.
The burden of proof can be different depending on the situation. In criminal trials, for example, the burden of proof is on the prosecution to prove beyond a reasonable doubt that the person they are accusing is guilty of the crime. In civil cases, the burden of proof is on the plaintiff (the person who filed the lawsuit) to prove their case.
So, the burden of proof is like a rule that helps us figure out who has to prove what in a debate or an argument. It's important to remember that if you are making a claim, you have to provide evidence to back it up, otherwise, people might not believe you.