Think of the number of apps on your phone that doesn't require internet access in one way or another. Now take out all the ones that came pre-installed with the phone. Chances are, the list has decreased to zero or you can list them all on one hand. You're building apps for smartphones, devices that are, by definition, built to connect to a network and interface with it. Therefore, knowing how to implement networking is critical to your success as a developer.
Before we begin, note that your app requires the following permissions in the manifest to able to make networking calls: