The Fission Theory: This theory proposes that the Moon was once part of the Earth and somehow separated from the Earth early in the history of the solar system.
When you actually use that class to make a THING, this is what you make. A method is a bit of code that can be called when needed (often as part of an class, but not always) Here's an example: I write a class called Ball. In my main code, I then write a=Ball.new, b=Ball.new, c=Ball.new.
Difference between a class and a set. I know what a set is. I have no idea what a class is. As best as I can make out, every set is also a class, but a class can be larger than any set. This obviously makes no sense whatsoever, since sets are of unlimited size.