According to the documents of Google Maps for Android V2:
An info window allows you to display information to the user when they
  tap on a marker on a map. By default, an info window is displayed when
  a user taps on a marker if the marker has a title set. Only one info
  window is displayed at a time. If a user clicks on another marker, the
  current window will be hidden and the new info window will be
  displayed. You can show an info window programmatically by calling
  showInfoWindow() on the target marker. An info window can be hidden by
  calling hideInfoWindow().
You can show the info window like this:
Marker marker = myMap.addMarker(new MarkerOptions()
                     .position(latLng)
                     .title("Title")
                     .snippet("Snippet")
                     .icon(BitmapDescriptorFactory
                     .fromResource(R.drawable.marker)));
marker.showInfoWindow();