Okay kiddo, let me explain what a category of elements means.
Imagine you have a bunch of toys - cars, dolls, puzzles etc. Now, we can group these toys based on some common features like their size, color or material. For example, we can put all the red cars in one group, all the wooden puzzles in another group and so on.
Similarly, in math, we can group things together based on certain properties they have. This group of things is called a category. And the things inside this category are called elements.
For example, let's say we have a category of animals. Some of the elements in this category could be cats, dogs, birds, and fish. All these elements have some common features - they are all living creatures, they have different types of bodies, and they may have different ways of moving or hunting for food.
So, a category of elements is like a group of similar things that we can study together and understand better. It helps us organize our knowledge and make connections between different things.