MobileApplication represents the out-of-box mobile application that runs on your device or emulator. Through MobileApplication class you can get hold of the a Project that's currently opened by the application. To get a collection of tasks and project extensions that are available for that mobile project, use ApplicationExtensions.

To learn more details on task, see Task.

For more information on Project Extension, see ProjectExtension.

Gps devices are heavily used in field data collection and feature inspection, you can access Gps settings within application framework as well. MobileApplication exposes GpsConnectionManager property, through which you can get Connection object. Note that Connection class is defined in ESRI.ArcGIS.Mobile.Gps namespace from core mobile framework. Once you get Gps Connection, you can access various location information from your Gps unit, including FixStatus, FixSatelliteCount, Altitude, Speed, Latitude, Longitude, and so on. This information can be used by either built-in tasks or your customized tasks/project extensions.

Moreover, you can directly open Gps port by calling StartGps, or close Gps port by calling StopGps.

At the core of application design, a Task is split into a series of pages that forms a complete field workflow. Therefore, there is often a need for developer to navigate user from one page to the other. MobileApplication class provides two methods for such purpose -
Transition and ShowDialog. Transition is used for transitioning user from one Page to the other, while ShowDialog shows user a form that has a dialog look-n-feel. An example of a dialog would be a settings dialog, or a login dialog that user needs to complete before doing something else.

System.Object
   ESRI.ArcGIS.Mobile.Client.MobileApplication

Reference