The concept of "Class" can be easily modeled thinking to a C struct
containing data members and a pointer to a struct containing function pointers (the v-table), where all functions have a "hidden" parameter Class* this
.
That said, if you are already familiar with struct, pointer and function pointers, classes are nothing "misterious".
Everything else is "art of usage" and is not itself related to the class concept itself but to how they can be arranged to have an effective maintainable code.
At this point you can
- try yourself to code a C program designed tat way (noting complicated, just to get the clue) or
- forget about C itself, and try understand how the concept should be used (rather then for what it technically is).
For the last point the Koenig and Moo "Accelerated C++" book can be a good starter: it does not consider C, but how C++ and it's library should be used, and -after going deeper and deeper in detail- show where those concepts come from.