Common sense reasoning means using the things you already know to figure out something new. It's like when you see a cat and you know that cats like to play with strings and chase after mice. So, if you see a string on the ground, you might think the cat will want to play with it.
Common sense is like a big library in your brain where you keep all the things you have learned about the world. You use this library to make guesses about what might happen next based on what you already know. That's why it's called common sense- because it's things that most people already know.
Sometimes when we don't have enough information to know for sure what will happen, we can use our common sense to make a good guess. For example, if it's cold and rainy outside, we know that it's probably not a good idea to wear shorts and a t-shirt. We use what we know about the weather and how to stay warm to make a good guess about what to wear.
In the end, common sense reasoning helps us make decisions every day. It helps us figure out what to do based on what we know about the world. And as we learn more and more, our common sense library gets bigger and we can make even better decisions!