Stamped paper is a special kind of paper that has a special mark on it that shows it has been officially approved by the government. This special mark is usually a stamp with a picture on it and it means that the person who bought the paper has paid a fee to the government for using it.
It's like when you go to a store and you want to buy candy. Before you can take the candy home, you have to pay for it. Stamped paper is kind of like that. If you want to use this special paper for something like writing a legal document, you have to pay the government a fee first.
The government puts a stamp on the paper to show that you paid the fee. Once you have the stamped paper, you can use it for things like writing a will, a contract, or a marriage certificate. And because it has the special stamp on it, people know that it's official and legal.
So stamped paper is basically a special type of paper that you have to pay the government for before you can use it for important things.