As an ancient marina, the concepts of Ruby, and OPPS originally fail to easily register on my consciousness. The following is the degree to which I currently understand them as applied to SUs Ruby API.
A class is the generic form of an object. Objects within a class share the same class characteristics, the differences between objects are found in their variable differences. A class "box", results in objects, that differ in height, width, or length.
Methods nare procedures that dertermine a variable's value. For example, the boxes height = volume/(width*length).
A SU Ruby plugin is a program that utilized the SU Ruby API to affect a SU model.