The data tab visualises the current Data sets and their contained data. Read a bit more about local data storage here
Sets are outlined in a table. The table shows their set names, the number of records contained within the set and a couple of actionable buttons to the right.
You can view a set's data by clicking the "view" button to the right of the set, or clear the entire set and its data by clicking the "clear" button.
Warning: you can't undo a clear, so make sure you no longer need the set and its data before using this functionality.
As well as viewing a set's data from this table, you can also view it by clicking on the top right button in a related data message in the messages tab. So long as the set still exists you will be taken straight to the sets data page.
Viewing a set will take you to its records page where it will dump the entire contents of its records into an expandable object view. Here you can expand/contract various nodes and explore the set thoroughly.