Okay kiddo, so a functional equation is like a special math rule that helps us understand how different things are related.
An L-function is a fancy function (like a machine that does math) that tells us something about a mathematical object called a "number field." We won't get into what a number field is, but trust me, it's important for understanding L-functions.
Now the cool thing about L-functions is that they have a special functional equation. This equation tells us how the L-function behaves when we change certain things about it.
It's like if you have a toy car and you want to see how it moves if you put different wheels on it. The functional equation is like the rule that tells you how the car will move with different wheels.
For mathematicians, the functional equation of an L-function is really important because it helps them understand some very complicated ideas in number theory. But for now, just remember that it's a special rule that helps us play with L-functions and understand them better!