The name of the file is kept from the old buildsystem so that developers don't need to change so much in their own behaviour.
pakfire-builder build path/to/makefile/makefile.nm
A very nice feature for doing first steps is the shell. One can easily set up a build environment and get a shell in it. After that one can do whatever one may think of. E.g. modify a package, create a new one, etc.
pakfire-builder shell path/to/makefile/makefile.nm