A Service helps you to execute tasks in the background. Like downloading a file or tracking user location changes.
It is an Application Componenet with no user interface. It has a simple life cycle and comes with a set of features.
There are two types of Services
Bound Service This kind of service is bound to a component like an Activity and runs as long as the Activity runs.
Started Service This kind of service can run indefinitely. Even when the Activity that started is is destroyed.
You can create a new service by extending either the Service Class or the IntentService Class.
IntentService allows you to create a started service.
In the video you will learn how to get started by creating an IntentService.
Source Code is available here
Why Android 