Okay, kiddo, this is a big topic but I'll try to break it down for you.
A long time ago, people who looked different from each other were often put into groups based on things like their skin color, hair type, and other physical features. These groups were called "races".
Back then, some people believed that certain races were better than others, based on things like their culture or where they came from. This way of thinking is called "racial hierarchy".
For example, some people thought that white people were the best race and that black people were inferior. They used this idea to justify treating black people unfairly, like making them slaves or not letting them vote.
Over time, scientists and researchers started to study race more closely. They looked at things like genetics and biology to try to understand if there really were big differences between races.
What they found was that there is actually very little difference between people from different races. Differences in skin color and hair type are just minor variations, like some people having brown hair and some people having blonde hair.
So nowadays, most people don't think about race as a way to sort people into groups or decide who is better than others. Instead, we focus on treating everyone with kindness and respect, no matter what they look like or where they come from.