Okay, let's pretend you have some toys that you really like to play with. But, there are some other kids nearby who also want to play with your toys. You might not want to share your toys with those other kids, because you really love your toys and you don't want them to get lost or broken.
In the same way, sometimes there are groups of mathematical objects (like symmetries or functions) that we really like to study. But, when we want to study these objects on a bigger stage (like a bigger group or a bigger space), we might need to share them with other groups.
That's where Clifford theory comes in. The idea is to take our original group (with our favorite objects) and figure out how it relates to a bigger group that we want to study. We do this by "lifting" our original objects up to the bigger group, like how you might lift your toys up to a higher shelf to keep them away from other kids.
But, just like how your toys might look different up on the shelf, our objects might look different when viewed from the perspective of the bigger group. Clifford theory helps us understand these differences and how we can still use our original objects to learn about the bigger group.
So, in a nutshell, Clifford theory is a way of understanding how our favorite mathematical objects relate to bigger groups, and how we can study these bigger groups without losing sight of our original objects.