So, there are some old stories from a long time ago that people in India used to tell each other called the Upanishads. And the Principal Upanishads are the most important and famous ones.
These stories are about really big ideas, like what happens after we die, what is the meaning of life, and how the whole universe and everything in it works.
Some of the stories are really hard to understand, but they can help us learn a lot about ourselves and the world around us. They also teach us to be kind to others, and to appreciate the beauty of nature.
Overall, the Principal Upanishads are a really cool and important part of Indian culture and history!