When a sku without a description is entered into the transaction window, the Change Description window will automatically pop up and prompt you to enter a description.
Once entered into the transaction, the description of the item can be changed again using the Miscellaneous tab. First either press F12, or use the button on the bottom of the screen.
This will bring up the Miscellaneous tab on the right hand side of the screen. Now either press Shift-F10, or use the
This will bring up the Change Description window. Simply type the item's new description into the empty field.
Once you have entered the new description, press the button to apply your changes.