The illustration shows the Edit Join Column window.

There are two columns.

On the left, the column is labeled Source 1. In a selection button below the label, CUSTOMERS is selected.

On the right, the column is labeled Source 2.  In a selection button below the label, Create Table is selected.

In the column on the left, CUST_ID is selected from a list of Join Columns. On the right, CUST_ID is selected from a list of join columns.

Below the two columns, an Add button is highlighted. An arrow extends from the button to a table below it that contains three columns, labeled Column 1, Column 2 and Join Type.

The table contains three values, respectively, CUSTOMERS.CUST_ID, Create Table.CUST_ID and Inner. 

Below the table, the OK button is highlighted.