The little tool is accessible via the “Tools” menu added to the DbEditor.
Once you are connected to a database, just click on the menu item and a window will display the SQL needed to create the missing indexes.
It is indeed about the DB native indexes.
There has been quite a few indexes created for Belfius overall, not only in search but in entity lists as well, except for the Belfius specific ones they are all available in standard in the SYS_INDEXES table.
If you are wondering exactly which ones are new compared to an older version at a client, the easiest is to compare the XML structure files with SVN diff.