Building an app that communicates with a server

Building an app that communicates with a server

Im new to programming in general and am currently trying to get started
building my first mobile app on android.I am thinking of creating an app
which would send requests to a server, which would then process it and
load the data in the app, which the user would then view.
I have the following questions:
Communicating with the server
How would i program the app so that it is able to communicate with the
server (I'm planning to use a web host like godaddy/hostgator etc).
Logging in & Identification
How would i go about uniquely identifying each user of the app?Would it be
possible to identify and create an account for any user who downloads my
app from the marketplace and runs it for the first time(Maybe through the
gmail account they use for the android marketplace?) or would i have to
make each user manually sign up and login the first time they run my app?
I would appreciate it if someone could tell me the best way to get started
and how best to go about developing such an app.
Thanks!