This article explain the usage of IntentService class in android SDK to perform background processing to offload tasks from an application’s main thread (Your activity).
when IntentService jobs done, the results are sent back to the activity.
Article Difficulty: 
URL Parameters are sent to php like:
http://www.example.com?param1=true
when you work with URL parameters you should validate them first.
you can read part 1 here.
You may reach a point where you need to transfer data from a server (web-service) to a an android client. although, there are many ways to achieve that goal, one of the simplest is using JSON. JSON is better then XML in terms of small bandwidth footprint. it has a lot of libraries for every available platform, so it makes the best solution for server-client communication.
