You have selected the Outer and Inner Sources to be Blended into a single dataset, and chosen to add a Condition to join the two sets of data.

SELECTING COLUMNS

The screen displays a List of the Columns that are from the 'Outer' data source, selecting one of these Columns will change the 'Inner' list of Columns to show the matching columns from the Inner Data Source.

It is possible to use filter the column list by using the boxes above the list of columns.

Next Select the Column from the Inner List and Press OK to confirm the Join