A simple example of a class procedure

This is probably a really basic question, but all the examples that I find involve way more than I need.  All I want to do is learn how to create a class procedure.  And then...How to call it.
As an example, A + B = C is the procedure.  I would create a class.  Right?  Then do I name the procedure and put it in the class?  Or create a new class for each procedure?
Then I would want to, on a local level, substitue values for A & B to return C. 
So, if the public procedure exists, how to I call it?
I know that this is really simple stuff, but I need examples to be simple.
Thanks,
Carthalion 
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