What are the differences between developing custom programs in classic mode and native mode (v8 and v11)

Can anyone help me? I'm learning how to develop in a sage X3 Version 8, using windows, screens, object, etc.

but later I will work with X3 Version 11, in this version I will work the same way? I'm seeing these Classes and Representations, I will use that instead of windows, objects etc...?

Grateful if anyone understand my question