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.
In C#, they are interchangeable (although method is the proper term) because you cannot write a method without incorporating it into a class. If it were independent of a class, then it would be a function. Methods are functions that operate through a designated class.