sorry if this is a dumb question but every once in a while i see something on the iPhone that i click and don't know what it does. when i go on the maps thing and i am looking at a map of how to get from a place to another place.....on the bottom right is a little picture of a car and i click it and it turns a darker blue and then i click it and it goes back to lighter blue but i don't see anything happen...what does it do!