So imagine you have a bunch of toys (let's call them numbers) and you want to be able to play with them in different ways. But sometimes it's hard to figure out how to play with them in different ways because they look different or act differently.
Now imagine you have a special grown-up (mathematician) who knows how to group these toys together based on how they act when you play with them. This grown-up groups them into different kingdoms (fields), depending on how the toys behave when you play with them.
But then, the grown-up realizes that sometimes these toys can actually be played with in different ways depending on where they come from or how they look. This is where Galois Theory comes in.
Galois Theory helps the grown-up understand how these toys can move between different kingdoms (fields) depending on some special rules (automorphisms). Think of these rules as the special way you have to hold the toy or the special word you have to say to make it work differently.
So now the grown-up can play with these toys in even more ways by understanding how they move between kingdoms (fields) and what special rules need to be followed to make them work differently. Pretty cool, huh?