All of the data sources and queries you have defined for the current report will be listed here. If you want to add a new data source, click the leftmost icon (the yellow cylinder) and select the data source type from the ensuing drop-down menu. To add a new query to an established data source, right-click the data source and then select Edit DataSource from the context menu. To delete a data source, select it, then press the Delete key, or right-click it and select Delete from the context menu.