Have you ever spilled something on your shirt and tried to get the stain out with soap and water? That's kind of like what happens with wood pulp when it's bleached.
Wood pulp is made from trees, and it's used to make things like paper and clothing. But before it can be used, it needs to be cleaned up so it's nice and white.
Bleaching is a process where chemicals are used to make the wood pulp nice and bright. Think of it like washing your hands with soap and water to get rid of dirt and germs. Except instead of using soap, they use chemicals like chlorine or hydrogen peroxide.
First, they mix those chemicals with water and add the wood pulp. Then, they let it sit and soak for a while so the chemicals can do their job. The chemicals break down all the stuff that makes the wood pulp look brown or gray, like dirt and other impurities.
After a while, they rinse off all the chemicals and clean water is added. The wood pulp is now much cleaner and whiter than before! From here, it can be used to make paper, clothing, and more.