Most of the time, the LEDs will not light up at all. This is to save power, since the device will most likely not be visible when installed. When power is first applied, the green led will continuously flash for 1 minute, or until the device goes in to low power mode. During this time, if any errors occur in either the upload, or any tasks that run, the red LED will light up (both LEDs will turn off when going into low power mode).
The button is used for testing purposes. A short button press will execute whatever is programmed as task 1. Again, the green LED will flash until the device goes to sleep (this may be a very short period of time), and the red LED lights up if any errors occur. A long button press (>3 seconds) will do the same thing, but also connect to the server on completion.