iPhone's Maps app gets where you need to go by providing driving directions and giving you the latest traffic info. You can get route maps and driving directions to any location from any other location in a couple of ways.
If there's a pushpin already marking your starting or ending location, do the following to find some driving directions:
Tap the pushpin.
The name or description of that location appears.
Tap the little > in a blue circle to the right of the name or description.
The item's Info screen appears.
Tap the Directions to Here or Directions from Here button to get directions to or from that location, respectively.
When you're looking at a map screen:
Tap the Directions button at the bottom of the map screen.
The Start and End fields appear at the top of the screen.
Type the start and end points.
Alternatively, select them from your bookmarks, recent maps, or contacts, if you prefer.
If you want to swap the starting and ending locations, tap the little swirly arrow button to the left of the Start and End fields.
Weird but true: If you type the end location, you'll have to tap the Route button before you can perform the next step; but if you select the end location from your Bookmarks, Contacts, or Recents list, the Route button doesn't appear and thus doesn't need to be tapped before you perform the next step.
When the start and end locations are correct, tap the Route button in the bottom-right corner of the screen.
The route map appears.
If you need to change the start or end location, tap the Edit button in the top-left corner and type a new start or end location in the appropriate field.
Tap the Start button in the top-right corner.
The Maps app gives you turn-by-turn driving directions. The two arrows in the top-right corner take you to the next and previous step in the turn-by-turn directions.
If you prefer your driving directions displayed as a list with all the steps, tap the curling page button in the lower-right corner, and then tap the List button in the list that appears.
When you're finished with the step-by-step directions, tap the Search button at the bottom of the screen.
You return to the regular map screen and single search field.
The iPhone can speak directions if you use one of several GPS apps, such as TomTom U.S.A., Navigon MobileNavigator, or MotionX GPS Drive, which are all decent. Plug the iPhone into a power outlet if at all possible while driving because such apps can quickly drain the battery.