Self-sufficiency means being able to take care of yourself without needing help from anyone else. It's like when you learn how to tie your own shoes or dress yourself all by yourself - you don't need anyone else to do it for you anymore!
Self-sufficiency is important because it makes you feel capable and independent. If you're self-sufficient, you can take care of yourself in many different ways like cooking your own food, growing plants to eat, or fixing things around the house. You can pretty much do whatever you need to do without having to depend on other people.
Being self-sufficient takes time and effort to develop. You have to learn new skills and practice them until you get good at them. You also need to have the right tools and resources to be able to do things on your own. But once you've become self-sufficient, it's a very useful and rewarding thing to be able to do!