Enter from the left menu: Tools > Rankings Discovery.
You'll get to the Rankings Discovery section, PRT will display discovered ranked terms.
Single URL: Select a URL, view the discovered ranked terms and their details (rank group, device, engine, last time it was updated, etc...), select the terms you wish to add for tracking, and click the Add button (at the top/bottom).
Multiple URLs: The data that is displayed is for all the URLs in your account, but you can also select a group or a URL at the top to display specific discoveries.
Click on terms you want to add for tracking in the left box (of each URL) and move it to the right box, than when finished click "Add" on the right bottom of the page.
For each URL will be displayed 200 terms maximum, and you can view all the discoveries from the Single URL tab.