In an emergency lift the handset and dial the emergency number for your locale, for example 999. If you need to dial a code when calling an external number, you will also need to dial that code before calling the emergency number.
Note that depending on your phone type and configuration the call may not complete automatically once you have finished dialling. For example, you may need to hit the OK or Confirm key once you have dialed the number.
Depending on the configuration of your telephone service, making an emergency call may trigger a notification to be sent to someone in your organisation to alert them that you have made an emergency call. This may be done to ensure that the emergency services can be directed to the correct location on your business premises or to discourage the making of hoax calls.