DFT or HF calculations
Nothing simpler!
The input files consists of two sections:

A Fortran namelist starting with
&molgw
and ending with/
. Fortran syntax is applied here. Comments are marked with!
. A comma,
is a valid delimiter. All the existing input variables are listed here. 
A list of atoms, which is very similar to an xyz file
There exists a comprehensive list of all the input variables in ~molgw/docs/input_variables.html
,
but for a DFT calculation of water, the input files is as simple as:
&molgw
comment='H2O within BHLYP' ! an optional plain text here
scf='BHLYP' ! 'HF' gives HartreeFock
basis='ccpVTZ'
auxil_basis='ccpVTZRI'
natom=3 ! Atomic coordinates are in angstrom, unless otherwise stated
/
O 0.000000 0.000000 0.119262
H 0.000000 0.763239 0.477047
H 0.000000 0.763239 0.477047