The way it works is quite simple. The power button remains depressed while the machine is being used. You can then push the espresso button to pump water through the portafilter holder or push the steam button and steam your milk. There is an LED to indicate when the machine is ready - water has to be at the right temperature / pressure to make good espresso.
What you do not do, however, is run water through the portafilter holder (also helps make better espresso by keeping it warm) and then push the on/off button instead of the espresso button - and then wonder why the 'ready' light isn't turning on after five or so minutes!
Oh, brain... where are you this morning?