@Halait-Ge : Here is something that worked for me. The developers guide provides a list of other commands that may be useful.
Sample macro file:
# one neutron spectra and other monoenergetic Cs-137 gammas
# source-1
/gps/source/add 1.
/gps/particle neutron
# pos/shape info
/gps/pos/type Point
/gps/pos/centre 10 0 0 cm
# angular distribution
/gps/ang/type iso
/gps/ang/mintheta 90 deg
/gps/ang/maxtheta 125 deg
/gps/ang/minphi -90 deg
/gps/ang/maxphi 90 deg
# energy distribution
/gps/ene/type User
/gps/hist/type energy
/control/execute spec.dat
# source-2
/gps/source/add 1.
/gps/particle gamma
# pos/shape info
/gps/pos/type Point
/gps/pos/centre 20 0 0 cm
# angular distribution
/gps/ang/type iso
/gps/ang/mintheta 90 deg
/gps/ang/maxtheta 125 deg
/gps/ang/minphi -90 deg
/gps/ang/maxphi 90 deg
# energy distribution
/gps/ene/type Mono
/gps/ene/mono 0.6617 MeV
/gps/source/list
/control/verbose 2
/run/verbose 2
/event/verbose 0
/run/beamOn 10000
Sample spec.dat:
/gps/hist/point 0.01 0
/gps/hist/point 0.25 0
/gps/hist/point 0.35 0
/gps/hist/point 0.45 0
/gps/hist/point 0.49 0
/gps/hist/point 0.5 1