Alright kiddo, let me try to explain what a nil ideal is in a way you can understand.
You know how sometimes you have a bunch of toys that you don't use anymore but you still have them in your room? Well, sometimes in math we have "toys" that we don't use anymore, but we still keep them around for important reasons.
A nil ideal is like having a toy box filled with broken toys. Even though they are broken and you can't play with them anymore, they are still in your toy box taking up space. In the same way, a nil ideal is a set of numbers that when you multiply them together, they become zero.
Now, having a toy box full of broken toys might not be very useful, but in math, nil ideals are very important when we study something called rings. Rings are just like a box of toys, but instead of playing with them, we use them to solve problems.
So, nil ideals are like broken toys taking up space in our box of toys, but they are important broken toys that help us solve problems.