The commandline synopsis for basic usage is
fastdep [--version] sourcefile...
fastdep --version will show version information and a short copyright statement and exit immediatly.
To produce dependency information for two files named file1.cc and file2.cc, execute fastdep file1.cc file2.cc from the shell.
The result will be written to standard output. For example it could be
file1.o: file1.cc \ header1.h \ header2.h \ header3.h file2.o: file2.cc \ header1.h \ header3.h \ header4.h
To save the output, use your shell to redirect standard output to a file which you can include in a makefile.