There really is no point in using the GWL without Guix. If you
already have a Guix installation, you can install the GWL with
guix install gwl.
The Guix Workflow Language uses the GNU build system. To install it from a release tarball just unpack it and run the usual commands:
./configure make make install
If you want to build the sources from the source repository you need to
bootstrap the build system first. Run
autoreconf -vif first and
then perform the above steps.
Note that in order for Guix to learn about the “workflow”
sub-command provided by the GWL, the guix/extensions directory
provided by the GWL must be added to the list of directories in the
GUIX_EXTENSIONS_PATH environment variable.