This Step by Step Tutorial teach you how to get user current location using GPS or Network in android app. And how to add a new Google API Key.
You can get source code of this tutorial from
GPS or Global Positioning System is a network of orbiting satellites that send precise details of their position in space back to earth.
LocationManger class provides access to the system location services. These services allow applications to obtain periodic updates of the device’s geographical location, or to fire an application-specified Intent when the device enters the proximity of a given geographical location.