...
One way to get started with OOP is the DevRoadmaps Clarion Library (DCL), our open source repository of Clarion code. There's a lot of terrifically useful code in the DCL, and you'll need some basic OOP concepts under your belt to make full use.
...
On the other hand, business logic in classes can be tested much more easily. I use ClarionTest for this (included in the DCL) and I'll have some docs up soon under the DCL page.
Reusability
Embed code isn't reusable - it just sits at that embed point. (Okay, if your embed code is a routine or a local class, it's reusable within that procedure. But not elsewhere.)
...
Separating the class header I (the declaration) from the implementation makes it easier to distribute classes in binary form, either for convenience or to protect intellectual property. To use a class you always need the class declaration in source form, but the implementation can be either source or binary code (e.g. a standalone LIB or LIB+DLL).
Using classes
You now have enough information to start using classes others have created. Feel free to download the DevRoadmaps Clarion Library and try out some of the classes. Probably the easiest place to start is with the DCL_System_String class.
...