N-ary associativity is a rule in math that helps us group things together in a specific way. Imagine you have a bunch of toys, like cars and blocks, and you want to put them in groups. If you use n-ary associativity, you can group them in any way you want, as long as you follow some rules.
These rules say that if you have three or more things that you want to group together, you can do it in any order, and the result will always be the same. For example, if you have three cars and you want to group them, you can do it like this: (car1+car2) + car3, or like this: car1 + (car2+car3). Even though you grouped them differently, the total number of cars is the same.
N-ary associativity is like a helpful tool that lets us group things together in different ways but still get the same result. It's kind of like playing with different toy combinations, and you get to choose how you want to play with them.