Chemsseddine,
Take a look at the User Guide's Section about Event handlers.
It highlights 3 different methods of adding event listeners:
- through configuration
- engine-wide listeners at runtime through the API
- and listeners added through specific process definitions
Use this as a starting point, but please come back if you have any further questions 
-JEarles
As far as I understand, the event listener is listeneing to general event like ( task completed or Variable created) is it possible to make the event listener on specfic event like specifi task completed or do I have to use the task listener , I really like the event listener and the possibility to throw an event back in Alfresco process services but I want to use it for specfic event
