The United Nations System of National Accounts is like a big book that helps countries keep track of all the money they have, how they spend it, and how much they make. It's kind of like if you had a piggy bank, and every time you got some money, you wrote it down in a notebook, then you wrote down everything you spent your money on. The United Nations does the same thing, but for entire countries.
The book is divided into different sections, and each section has different information about the money that a country has. One section will have information about how much businesses in the country are making, another section will have information about how much the government is spending on things like schools and hospitals, and another section will have information about how much people in the country are making.
The United Nations wants every country to use the same system to keep track of their money, so that it's easier to compare and understand how different countries are doing financially. It's like if you and your friends all used the same system to keep track of your money, you could all compare and see who is saving the most or spending the most.
By using the United Nations System of National Accounts, countries can figure out how well their economy is doing, and use that information to make decisions about things like taxes, employment, and investments. It's like if you knew how much money you had in your piggy bank, you could decide if you wanted to buy a toy, save it for later, or share it with your friends.