Attach Columns to Input Values
The final step is to attach your test step inputs and verifications to the columns of your data source. Let's look at a Set Text as our first example:
- In the properties of a Set Text test step, you will find a Data Driven section.
- Click on the down arrow to open the Data Driven Editor dialog.
- Click the Text node to select it.
- Then enter the name of the column you want to use to set the text when that step runs.
- In this example, the Input A column is used. Type $(Input A) into the text field at the bottom and press Set.
When the test runs, that input field will be set to each value from the Input A column instead of what was actually typed into the search field when the test was recorded.
Most action steps have at least one property that can be bound to a column from your data source.

Update: R1 2012 SP2
As of version 2012.1.719, simply select a column name from the Value drop-down. This list will not include columns from the parent data source of a test as step.
If you've Set an Extracted Variable in Code or wish to access the data source of a parent test, type the variable name in the text box (without the $ notation):