Service Delegates are the Java representation of the Service Tasks in your BPMN model.
You link a Service Delegate to a certain Service Task by selecting the Service Task
in the Camunda Modeler and adding a Java class to the Implementation field.
Make sure you use the fully qualified class name. Like this:
org.package.myClass
All that is left is for your Java class to extend AbstractServiceDelegate and override the doExecute method.
This is the place where you can put your actual business logic. The method will be called when the BPMN process execution
arrives at the Service Task your Service Delegate is linked to.
The constructor of your delegate class should also forward a ProcessPluginApi instance to its superclass constructor.
You can learn more about the ProcessPluginApi here.