The Alarm Button is used to cancel an Alarm State. It will not do anything to the Surveillance Mode.
When the Surveillance Mode is either Armed or Partially Armed and a sensor is tripped the Alarm State will be activated.
When that happens the The alarm is activated flow card will be triggered and the state of the Alarm Button will be set to Alarm*.
When you click the Alarm Button in that state the Alarm State will be cancelled but the Surveillance Mode wil remain.
Can you please show me (screenshot) what part of the instructions is not clear?
(* it is unfortunately not possible for community developers to show a state on a device tile, Athom does not yet provide such functionality: https://github.com/athombv/homey-apps-sdk-issues/issues/17 please ask Athom to add this functionality)