The protected keyword works in a class just as the private keyword outwards. The only difference is that an inheriting class will get the protected variables tucked into its private section, so that the subclass can use it and alter it at will. (If you do public inheritance)

As for the virtual keyword. If a class (A) is virtual it means a subclass (D) can have one or more superclasses (B and C) that inherit from that baseclass (A). Normally class D would have a problem trying to access variables and methods in the base class A since it "owns" several instances of it. With the keyword virtual you are guaranteed that every subclass that may, or may not, have multiple instances of same base class will in fact end up with only one.

Actually, the topics you ask about are very large. It is much easier to look up tutorials or articles on them if you couldn''t understand it from C++ Primer. Have you skipped some chapters or something? Last time I read the book it was very easy to understand. (Later I realised it wasn''t such a good book at teaching C++ since it teaches a lot of C... but it is still a great programming primer. So it should have no problems teaching you classes and inheritance. Actually, those parts are the strength of the book.)