When you tap the red button, the app gets your GPS position.
When you tap the center button, the app shows you a bird view of the subway map.
You can tap the in arrow to zoom-in on a specific location.
You can also tap the out arrow to zoom-out on a specific location.
When you tap the back button, the app closes.
When you tap the home button, the app stays open in the background.
You can also double-tap the map to zoom-in on a specific location.