The services directory page for a geoprocessing service provides all the information you need to include it in your application.
This includes the execution type which can be either synchronous or asynchronous. In the case of the PopulationSummary service seen in the following screenshot, it is a synchronous task. This means that once your application has executed, it won't do anything else until the results of the geoprocessing task have been returned. This type of execution is typically used only with tasks that you expect to execute quickly.
Asynchronous geoprocessing tasks are submitted as jobs and allow your application to continue functioning while the geoprocessing service is doing its work. When the task has completed, it notifies your application that processing is complete and the results are ready.
The other information you will need from the services directory page for the service includes the parameter names, the parameter...