When using a lookup field, you may want access to additional fields/columns in your popup window. You can add additional fields as columns to this window in order to sort through your records more efficiently. The example in this article is the Quote Lookup. Below you'll find a video showing an example of adding fields to the Staff Lookup Dialog.
- Navigate to Setup > Create > Objects > Click on the Object you are Looking up to (in this example: the Quote object)
From the managed page, hover over the 'Search Layouts' related list:
Click 'Edit' next to 'Lookup Dialogs'
You'll be able to add additional fields using the Add/Remove buttons, and adjust their order using the Up/Down' buttons.
Additionally, here is a short video you can follow along with: