This screen allows actions to be triggered based on pressing of the hardware buttons and some of the on-screen soft buttons.
The 0/Centre configuration on the left leads to the star menu on the right when the centre navigator button is pressed in the Calc application.
Note that not all buttons are present on all devices. Just ignore the ones you don't have. In particular, VolUp, VolDown, Side and Option Hard 1-4 (oHrd1-4 in Apt) buttons are probably only available on Treos.
The 'Powr' button trigger only activates when you turn the device off. To do things when the power is turned on, use the Events:Wake trigger.