Did you complete the step #1 (install Xcode, X11, and MacPorts)?
If so open a new terminal window and enter the command given to install the needed dependencies:
sudo port install libsdl-framework libsdl_mixer-framework libsdl_ttf-framework \
jpeg libpng XviD libtheora gtk2 gtkglext gtksourceview2 git p7zip python27 \
doxygen libsdl2 libsdl2_mixer libsdl2_ttf