I didn't run the examples in Qt, but I imported the libfreespace library. You have to add the library and the include-directory to your .pro file with something like
LIBS += -L$$PWD/../../../../usr/local/lib/ -lfreespace
INCLUDEPATH += $$PWD/../../../../usr/local/include
DEPENDPATH += $$PWD/../../../../usr/local/include (pathes probably needs to be modified according to where you installed the library)
Then you can include the library in your header file with
#include <freespace/freespace.h>
#include <freespace/freespace_util.h>
Is that sufficient informatio or do you need a full example?