The Data tab controls the way each field is stored in Modeler, which in turn has implications for how a field can be used. Generally, the measurement level determined by Modeler is appropriate, however if you need to change this for a field, check the field's Override box, then click in its Storage cell and select the appropriate storage option.
In this example, we do not need to change anything on this tab. In our own experience, often you might need to specify the appropriate format for date and time fields here:
As an aside, the Data tab of most source nodes functions more like the File tab of the Var. File node. Thus, this design of the Data tab in the Var. File source node makes it very easy to change the format of fields that you would otherwise need to change using a Filler node.
Let's click on the Filter tab to see the additional options.