The 'my location' icon shows where you are if you need to get your bearings. A green halo appears to show you roughly where you are if there's a problem finding your exact location. In densely populated areas, the accuracy is better, and the green halo is not as large.
Explore the map: You can move the map around by dragging your finger across the screen. The map is always oriented north.
See where you are right now: Tap the 'my location' icon.