Download either the .tar.gz or the .zip file and extract: e.g.
tar -czvf whap-src.tar.gz
This will create four directories: snphap-1.0, shaunlib, usat and whap2
cd to each in turn and type make. If you are using MS-DOS and DJGPP, then type make -f Makefile-msdos instead, except for the snphap-1.0 directory, where make should work just fine.
If all this works, then copy the files whap, usat and snphap to somewhere that is in your path -- then you are all set...
If by some chance the above step did not work, try
Ensure you have a C/C++ compiler on your system. For MS-DOS, I find DJGPP works well.
You might need to change the line of the Makefile from CXX=g++ to CXX=gpp if you use DJGPP.
When compiling in MS-DOS, you might need to erase the lines
$(LIB) : FORCE
cd $(LIBDIR) && $(MAKE)
from the Makefile in the whap2 directory. Then make sure you make shaunlib before whap.
Assuming you've managed to install a C/C++ compiler on your system, please feel free to drop me a line and
let me know the error message and the system you are using.