Hi @PratimaK16730164: “Data source property” corresponds to the property from the source (In your case the data page) and “Property” corresponds to the target where the value to be set (Property in case level page list which is configured as property for the Control).
In general, it is mandatory set at least one mapping for multi select control to work so that the selected items from the multi select will be updated in the page list configured as source of the multi select control.