Your teacher should have explained.
clang++ -o fig03_13 GradeBook.cpp fig03_13.cpp
clang++ GradeBook.cpp fig03_13.cpp -o fig03_13
ought to do it. That's your lines, but without the .h file.
Inside the cpp files you'll find a line
#include "GradeBook.h"
which is how it gets used.
Andy