Okay, so Ritsuryō is a big word that means a set of rules and laws created a very long time ago in Japan, like more than 1,000 years ago. It was created by the government to organize the country and make sure everyone behaves properly.
Think of it like when your parents make rules for you and your siblings to follow at home. The Ritsuryō was kinda like that but for everyone living in Japan at the time.
The rules covered a lot of things like how people should behave, taxes that needed to be paid, and how land was owned and used. The Ritsuryō also created a system for the government to run and made sure everyone had a job to do.
It was really important for Japan because it helped maintain peace and order, and made sure everyone had equal rights and laws they had to follow.