"invent"

Last evening, there was a big thunder and lighting when we drove home from a concert. Henry and I had a little discussion on collecting lighting and making use of it.
Caleb has read the book about thunder and lighting for many times, he seemed to be happy to see them in person. I also told him about "lighting conductor". When henry was talking about the effort "Benjamin Franklin" made to collect the lighting, caleb joined the conversation:
Caleb: Frankline?
Henry: of course, it is not Franklin the turtle, It is Benjamin Franklin
Caleb: who is he, and where do he live?
Henry: Benjamin Franklin is no longer alive, but do you know that he invented "lighting conductor"?
Caleb: what is "invent" mean?

I guess "invent" is still hard for him to understand. I had explained once "invent" to him. Obviously he did not quite understand. I need to use that word in our daily life to help him understand.