Using the Favorites feature is simple and an easy way to give a user custom filtering on data sources. You may have a Favorites list for each data source. To define Favorites you will need a Permanent Unique Key on the data source.

1) Define the data source - If need be, you can manually define a Permanent Unique Key by refering to the field which contains a unique value in each record. Records with no value or blank values are not legal in PUKs. Here's an example of what that definition might look like -

                                      ' item :guid '

2) Display the data - Define an action that triggers the adding to the favorites list - in the Events, apply ADD TO FAVORITES to the source table. This adds the key value on the selected record to your favorites on that data source. 

3) View the favorites list - Define a List Block for your Favorites list (this is exactly like any data view). Then filter the data at the point before you switch to the List Block - add a DEFINE A DATA SOURCE FILTER action on the data source, and set the field COLUMN to '(favorites)' in the drop down of field names. The List Block should now show any records you have added as a Favorite. To display something in the case where no Favorites have been added, be sure to define a message in the EMPTY RESULTS TEXT field on the List Block.

Note that Favorites remain defined after the App is closed, and will remain defined when the App is next launched.