Self-pollination means that plants can make babies without the help of bees or other insects. Just like how bees carry pollen from one flower to another, plants have their own special way of doing this.
When a plant wants to make a baby, it has to get pollen from its own flowers to its own eggs. So, the plant uses some of its own pollen and puts it in the right spot on its own flower. This way, the plant can fertilize its own eggs and make a new baby plant all by itself!
Think of it like taking some of your own toys and using them to create a new toy all by yourself without having to share with your friends. That's kind of what self-pollination is like for plants!