This publication was developed as an informational guide for soil moisture mapping at landscape level through a portable `backpack' cosmic-ray neutron sensor. This recently developed device monitors soil water content in a non-invasive way using background neutron counts. It is used to measure water content in the topsoil over wide areas, covering approximately 20 hectares with one single measurement. Through its mobility and combining series of measurements, this provides the spatial variability of the soil water content for better agricultural water management. The publication provides scientists, technicians and students with the necessary information, guidance and steps to calibrate, validate and deploy this portable cosmic-ray neutron sensor.