after you have selected the destination pull the iDrive knob to the left twice (or hit the nav button above the knob) and the last menu option will give you a list of all the turns from start to destination. As you scroll through each turn you will see the map on the right side of the screen. You can also push the iDrive knob to the right to select the screen and then rotate the knob to swithc the zoom level.

From the list of directions you can also select other routes (not sure how it picks the alternate routes)