CardParts are used for FactBoxes that don't require a list. CardParts display fields or perhaps a picture control. (NAV 2017 Help contains an example of including a DotNet add-in within a FactBox to display a chart). An example of the Customer Statistics FactBox (Page 9082 - Customer Statistics Factbox) is shown in the following screenshot:

ListParts are used for FactBoxes that require a list. A list is defined as columns of repeated data. No more than two or three columns should appear in a FactBox list. The following screenshot shows the three-column My Items FactBox ListPart (Page 9152):