Okay kiddo, let me tell you about Sierra Club! It's a big group of people who care a lot about nature and the environment. They want to protect things like forests, rivers, and animals from getting hurt or destroyed.
The Sierra Club was started a long time ago in 1892 by a man named John Muir. He was really interested in exploring and appreciating nature, and wanted to help other people do the same. Since then, lots of people have joined the Sierra Club to work together and make sure our planet stays healthy and beautiful.
Some things they do include going on hikes and camping trips to explore the wilderness, cleaning up trash in parks and rivers, and talking to politicians to try and make laws that will help protect the environment.
So basically, the Sierra Club is a big group of people who love Earth and want to take care of it!