If you are performing a Groundwater Analysis, and the Analysis Mode = Groundwater, then you will be able to assign the materials you have defined with the Define Hydraulic Properties option, to the corresponding soil regions of the model, with the Assign Properties option.
However, it is very important to note the following:
If you are performing BOTH slope stability and groundwater analyses, then the Assigning of material properties, should only be done ONCE. Remember that the STRENGTH properties and the HYDRAULIC properties of each material you define, "belong" to the SAME material.
Therefore, you CANNOT INDEPENDENTLY assign material strength properties, and material hydraulic properties, because the "materials" are actually the same.
When you assign strength properties, you are also assigning the hydraulic properties, and vice versa.
The Assign Properties option is made available in the Groundwater Analysis Mode, for convenience. For example, if you are ONLY performing a Groundwater Analysis, and NOT a slope stability analysis in Slide, then it is convenient to have the Assign option available in Groundwater Analysis Mode.
The process of assigning hydraulic material properties when the Analysis Mode = Groundwater, is the same as assigning material strength properties when the Analysis Mode = Slope Stability. See the Assign Materials topic for details.