The first time you launch the app is the slowest.
You should see the Debug pane appear at the bottom
of the window that looks something like the following:

    

    You can configure where the debug pane appears,
or even tear it off to its own
window using the gear to the right in the Debug pane bar.
This is true for any inspector in Android Studio.

Add a breakpoint on the counter++ line.

In the app, click the + button
(FloatingActionButton, or FAB, for short)
to increment the counter. The app pauses.

The following screenshot shows:
    
      Breakpoint in the edit pane.
      State of the app in the debug pane, when paused at the breakpoint.
      
this variable expanded to display its values.