Okay kiddo, so a blue law is a rule made by the government or the church that says you can't do certain things on certain days. It's called a blue law because it used to be printed on blue paper a long time ago.
For example, some blue laws say that you can't buy alcohol on Sundays or that stores can't be open before a certain time on Sundays. This is because Sunday is considered a day of rest and people should spend time with their families or go to church.
Some blue laws also say that you can't hunt or fish on Sundays, or you can't sell cars on Sundays. They are usually made to keep the community quiet and peaceful on that day.
Even though some blue laws are still around, they are not always enforced, and some have been changed or phased out. So, it's important to ask your parents or an adult if there are any blue laws that affect you.