There are a few C++ features, namely (single) inheritance and templates, which are easily abused, but can dramatically simplify an implementation if used properly. I describe the basic idea behind these ``dangerous but useful'' features here, in case you run across them. Feel free to skip this section -- it's long, complex, and you can understand 99% of the code in Nachos without reading this section.
Up to this point, there really hasn't been any fundamental difference between programming in C and in C++. In fact, most experienced C programmers organize their functions into modules that relate to a single data structure (a "class"), and often even use a naming convention which mimics C++, for example, naming routines StackFull() and StackPush(). However, the features I'm about to describe do require a paradigm shift -- there is no simple translation from them into a normal C program. The benefit will be that, in some circumstances, you will be able to write generic code that works with multiple kinds of objects.
Nevertheless, I would advise a beginning C++ programmer against trying to use these features, because you will almost certainly misuse them. It's possible (even easy!) to write completely inscrutable code using inheritance and/or templates. Although you might find it amusing to write code that is impossible for your graders to understand, I assure you they won't find it amusing at all, and will return the favor when they assign grades. In industry, a high premium is placed on keeping code simple and readable. It's easy to write new code, but the real cost comes when you try to keep it working, even as you add new features to it.
Nachos contains a few examples of the correct use of inheritance and templates, but realize that Nachos does not use them everywhere. In fact, if you get confused by this section, don't worry, you don't need to use any of these features in order to do the Nachos assignments. I omit a whole bunch of details; if you find yourself making widespread use of inheritance or templates, you should consult a C++ reference manual for the real scoop. This is meant to be just enough to get you started, and to help you identify when it would be appropriate to use these features and thus learn more about them!