The functionality of each button greatly depends on the app you are using and what is on the screen. Some apps like DMD2 allow you to fully configure each button on some sections (example: Roadbook), for sections where you cannot configure you can use this reference:

• Button A click – is usually Enter or Select for any dialog box, in the map view it toggle the follow location if nothing else is in the screen
• Button A long press – will jump to the bottom menu to change the current view
• Button B click – is usually an alternate function, in the map view for example it toggle the satellite layer
• Button B long press – is usually CANCEL if any dialog is on the screen, if no dialog is preset it will do another function, in the map for example it will do LOCK
• Top 4 Way Joystick – will be selection cursor when there is anything selectable on the screen, for the map it will be map panning
• Bottom 2 way switch – will do Zoom In and Zoom Out or Increase / Decrease if such dialog type is on the screen

Note that Button A and B usually have long press functions (unless configured otherwise – for example in the roadbook view where you can configure every button). Both the 4 way joystick and 2 way switch will not have long press actions but instead do repeat (again, unless if configured otherwise).