This tab is in the Debug tab.
The Foreign Keys tab assists in finding and changing data that is the target of foreign key references.
To find the records that reference a specific row, enter the table containing that row into the Table Name field, enter the ID of the row into the ID A field, and press the Show References to ID A button.
If you have part of a table displayed in the Query Results tab, you can pick out the ID from that row and put it into the ID A field by pressing the Take Selected ID to A button.
The ID B field works just like the ID A field, but with its own set of buttons.