For your 2008, be sure to look for an OBD
-II reader with the words "CAN" or "CAN-bus" because many of the earlier readers are not fully Controller Area Network capable. Price varies widely based on features. If all you want to do is read and clear trouble codes, get a simple one from Harbor Freight or equivalent. List price is $40 but they regularly go on sale for $30.
Any reader should come with instructions and a universal code list. Ford-specific codes that may not be included in that list can be found at several online sites. There are fancier professional style readers that show a short description on the display along with the trouble code but they are more expensive and not much of an advantage for occasional use.