•  Diff between Modules & Classes

Classes differ from standard modules in the way their data is stored. There's never more than one copy of a standard module's data. This means that when one part of your program changes a public variable in a standard module, and another part of your program subsequently reads that variable, it will get the same value. Class module data, on the other hand, exists separately for each instance of the class (that is, for each object created from the class).
By the same token, data in a standard module has program scope — that is, it exists for the life of your program — while class module data for each instance of a class exists only for the lifetime of the object; it's created when the object is created, and destroyed when the object is destroyed.
Finally, variables declared Public in a standard module are visible from anywhere in your project, whereas Public variables in a class module can only be accessed if you have an object variable containing a reference to a particular instance of a class.